Control device for ac rotating machine, and control device for electric power steering

ABSTRACT

A control device applies voltages to an AC rotating machine based on voltage command values on stationary coordinates. Currents in a plurality phases flowing the rotating machine are detected as detection currents. Coordinate conversion is applied to those detection currents based on any phase in the rotating machine, for generate detection currents on rotational coordinates. Voltage command values on the rotational coordinates are generated based on current command values on the rotational coordinates and the detection currents. Coordinate conversion is applied to those voltage command values based on the any phase, for generate first voltage command values on the stationary coordinates. Phases of one of the first voltage command values and generated second voltage command values on the stationary coordinates are corrected to generate the second voltage command values. One of the second and the first voltage command values are selected as the voltage command values on the stationary coordinates.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2018/008384 filed Mar. 5, 2018.

TECHNICAL FIELD

The present invention relates to a control device for an AC rotatingmachine, which is configured to control the AC rotating machine, forexample, a synchronous motor, and to a control device for an electricpower steering system, which uses the control device for an AC rotatingmachine.

BACKGROUND ART

In control for an AC rotating machine, coordinates to be used to treatcurrents or voltages, which are vector quantities, are broadlyclassified into two types of coordinates, which are stationarycoordinates and rotational coordinates.

As the stationary coordinates, there are known three-phase ACcoordinates directly treating values in three phases, for example, U, V,and W phases, two-phase AC coordinates to be used to observe a state onorthogonal stationary two-axis coordinates based onthree-phase/two-phase conversion, and the like. As the rotationalcoordinates, orthogonal rotational two-axis coordinates are well known.Among those orthogonal rotational two-axis coordinates, there are knowncoordinates rotating synchronously with a rotation position of an ACrotating machine, coordinates rotating synchronously with a frequencycommand value, coordinates rotating synchronously with estimated rotormagnetic flux or induced voltages, and the like.

There is known a control device for an AC rotating machine configured toprovide current command values on rotational coordinates when the ACrotating machine is driven, to thereby apply control so that currentvalues on the rotational coordinates of the AC rotating machine matchthose current command values. Hitherto, in order to obtain the currentvalues on the rotational coordinates of the AC rotating machine, therehas been used a method involving detecting, by a current detector,current values of the AC rotating machine as current values on thestationary coordinates, and applying coordinate conversion to thedetected current values. In this configuration, the control for the ACrotating machine is executed by calculating voltage command values onthe rotational coordinates so that those current command values matchthe detected current values, and using voltage command values in thethree phases on the stationary coordinates, which are obtained byapplying coordinate conversion to the calculated voltage command values,and voltage command values in the three phases, which are calculatedbased on the current values detected by the current detector (forexample, see Patent Literature 1).

The current detector is configured to detect currents in the threephases, for example, the U phase, the V phase, and the W phase. However,it is known that a phase having an undetectable current exists due toinfluence of switching noise depending on switching timings of switchingelements configured to apply the voltages to the AC rotating machine. Inthis case, hitherto, on the basis of the fact that the sum of thecurrents in the three phases is zero, the current value in the phasehaving the undetectable current has been estimated from the currentvalues in the phases having the detectable currents (for example, seePatent Literature 2).

CITATION LIST Patent Literature

-   [PTL 1] JP 5178768 B2-   [PTL 2] WO 2016/143120 A1

SUMMARY OF INVENTION Technical Problem

A control device for an AC rotating machine is sometimes used for, forexample, an electric power steering system mounted to a vehicle, forexample, an automobile. Noise emitted from the AC rotating machinemounted to the vehicle may give a sense of discomfort to a driver. Thenoise emitted by this AC rotating machine includes noise caused by thevoltage command values directed to the AC rotating machine.

A frequency of the noise caused by the voltage command values depends ona calculation frequency of the voltage command values. Therefore, thefrequency of the noise is increased by increasing the calculationfrequency of the voltage command values, that is, reducing an updatecycle of the voltage command values to a short cycle. The sense ofdiscomfort given to the driver by this noise can be reduced byincreasing the frequency of the noise.

However, as the update cycle of the voltage command values directed tothe AC rotating machine is reduced, a calculation amount per unit timerequired in order to update the voltage command values increases, andthus a load of the processing caused by the update becomes higher. Asthe load becomes higher, performance required of a processing device forexecuting the calculation, for example, a microcomputer, increases,which causes an increase in cost of the control device for an ACrotating machine. Thus, it is important to further suppress thecalculation amount per unit time in order to suppress the cost.

A difference in phase between the voltages and the currents changes inaccordance with a rotational speed of the AC rotating machine.Therefore, when the voltage command values in the three phasescalculated based on the current values detected by the current detectorare used to control the AC rotating machine, it is also required inpractice to address the difference in phase between the voltages and thecurrents.

The present invention has been made in view of the above-mentionedproblems, and therefore has an object to provide a control device for anAC rotating machine and a control device for an electric power steering,which are capable of reducing a sense of discomfort given to a human bynoise of the AC rotating machine while reducing a calculation amount perunit time.

Solution to Problem

According to one embodiment of the present invention, there is provideda control device for an AC rotating machine, the control device for anAC rotating machine including: a voltage application unit configured toapply voltages to the AC rotating machine based on voltage commandvalues on stationary coordinates; a current detection unit configured todetect currents in a plurality of phases flowing through the AC rotatingmachine; a first coordinate conversion unit configured to set thecurrents detected in the plurality of phases by the current detectionunit as detection currents on the stationary coordinates, and applycoordinate conversion to the detection currents on the stationarycoordinates based on any phase of the AC rotating machine, to therebyoutput detection currents on rotational coordinates; a current controlunit configured to output voltage command values on the rotationalcoordinates based on current command values on the rotationalcoordinates, which specify currents to be supplied to the AC rotatingmachine, and on the detection currents on the rotational coordinates; asecond coordinate conversion unit configured to apply coordinateconversion to the voltage command values on the rotational coordinatesbased on the any phase, to thereby output first voltage command valueson the stationary coordinates; a voltage command generation unitconfigured to set one of the first voltage command values on thestationary coordinates and second voltage command values on thestationary coordinates generated immediately before as target commandvalues, and correct phases of the target command values based on achange rate of the any phase, to thereby generate the second voltagecommand values on the stationary coordinates; and a voltage commandoutput unit configured to select one of the second voltage commandvalues on the stationary coordinates generated by the voltage commandgeneration unit and the first voltage command values on the stationarycoordinates generated by the second coordinate conversion unit, tothereby output the selected one of the second voltage command values andthe first voltage command values as the voltage command values on thestationary coordinates.

Advantageous Effects of Invention

According to the present invention, it is possible to reduce a sense ofdiscomfort given to a human by the noise of the AC rotating machinewhile reducing the calculation amount per unit time.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram for illustrating an overall configurationexample of a control device for an AC rotating machine according to afirst embodiment of the present invention.

FIG. 2 is a block diagram for illustrating an internal configurationexample of a current control unit 7 employed in the control device foran AC rotating machine according to the first embodiment of the presentinvention.

FIG. 3 is a block diagram for illustrating a configuration example of astorage unit included in a voltage command generation unit mounted inthe control device for an AC rotating machine according to the firstembodiment of the present invention.

FIG. 4 is an explanatory graph for showing a principle of phasecorrection executed in a voltage command calculation unit 91.

FIG. 5 is a block diagram for illustrating a configuration example ofthe voltage command calculation unit included in the voltage commandgeneration unit mounted in the control device for an AC rotating machineaccording to the first embodiment of the present invention.

FIG. 6 is an example of a time chart for showing operation examples ofrespective units included in the control device for an AC rotatingmachine according to the first embodiment of the present invention.

FIG. 7 is a graph for showing an example of a first U-phase voltagecommand value vu1* on stationary coordinates and a second U-phasevoltage command value vu2* on the stationary coordinates, which aregenerated when the control device for an AC rotating machine accordingto the first embodiment of the present invention is operated inaccordance with the time chart of FIG. 6.

FIG. 8 is a graph for showing an example of waveforms of three-phasecurrents and three-phase voltages different in phase from each other by10 degrees in a steady state.

FIG. 9 is a block diagram for illustrating a configuration example of avoltage command calculation unit employed in a second embodiment of thepresent invention.

FIG. 10 is an example of a time chart for showing operation examples ofrespective units included in a control device for an AC rotating machineaccording to the second embodiment of the present invention.

FIG. 11 is a graph for showing an example of a first U-phase voltagecommand value vu1* on the stationary coordinates and a second U-phasevoltage command value vu2* on the stationary coordinates, which aregenerated when the control device for an AC rotating machine accordingto the second embodiment of the present invention is operated inaccordance with the time chart of FIG. 10.

FIG. 12 is a block diagram for illustrating an overall configurationexample of a control device for an AC rotating machine according to athird embodiment of the present invention.

FIG. 13 is an example of a time chart for showing operation examples ofrespective units included in the control device for an AC rotatingmachine according to the third embodiment of the present invention.

FIG. 14 is a graph for showing an example of a first U-phase voltagecommand value vu1* on the stationary coordinates and a second U-phasevoltage command value vu2* on the stationary coordinates, which aregenerated when the control device for an AC rotating machine accordingto the third embodiment of the present invention is operated inaccordance with the time chart of FIG. 13.

FIG. 15 is a block diagram for illustrating an overall configurationexample of a control device for an electric power steering systemaccording to a fourth embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

A control device for an AC rotating machine and a control device for anelectric power steering system according to each embodiment of thepresent invention are described below with reference to the drawings.Herein, the same components or components that correspond to each otherare denoted by the same reference numerals.

First Embodiment

FIG. 1 is a block diagram for illustrating an overall configurationexample of a control device for an AC rotating machine according to afirst embodiment of the present invention. The control device for an ACrotating machine according to the first embodiment is configured tocontrol and drive an AC rotating machine 2. The control device for an ACrotating machine includes a voltage application unit 1, a positiondetection unit 3, a current detection unit 4, a first coordinateconversion unit 6, a current control unit 7, a second coordinateconversion unit 8, a voltage command generation unit 9, and a voltagecommand output unit 10. The AC rotating machine 2 is a synchronousmotor, for example, a synchronous electric motor. In FIG. 1, the ACrotating machine 2 is referred to as “synchronous motor.”

The current detection unit 4 is configured to detect currents to besupplied to the AC rotating machine 2, to thereby output current valuesas digital signals. In order to output those current values, the currentdetection unit 4 incorporates analog-to-digital (A/D) conversion units.The position detection unit 3 incorporates a resolver-to-digital (R/D)converter, and is configured to output a rotation position of the ACrotating machine 2 as a digital signal.

The first coordinate conversion unit 6, the second coordinate conversionunit 8, the current control unit 7, the voltage command generation unit9, an angular frequency calculation unit 60, and the voltage commandoutput unit 10 are each implemented by a digital circuit. The digitalcircuit is specifically, for example, a microcomputer. Those respectiveunits 6 to 10 and 60 are implemented by, for example, respectivesubprograms forming one program executed by the microcomputer. Theprocessing device configured to execute the program may be a processingdevice different from the microcomputer, for example, a processingdevice including a central processing unit (CPU), a random access memory(RAM), and a read only memory (ROM).

In the first embodiment, coordinates including U, V, and W phases areused as stationary coordinates. The voltage application unit 1 isconnected to the AC rotating machine 2 through three-phase currentsupply lines 11, and is configured to apply three-phase AC voltages vu,vv, and vw to the AC rotating machine 2 through the three-phase powersupply lines 11. The three-phase AC voltages vu, vv, and vw include aU-phase AC voltage vu, a V-phase AC voltage vv, and a W-phase AC voltagevw.

The voltage application unit 1 is configured to input digitalthree-phase voltage command values vu*, vv*, and vw* from the voltagecommand output unit 10, and to convert an internal bus voltage to thethree-phase AC voltages vu, vv, and vw based on the three-phase voltagecommand values vu*, vv*, and vw*. After that, the voltage applicationunit 1 applies the converted three-phase AC voltages vu, vv, and vw tothe AC rotating machine 2. The three-phase voltage command values vu*,vv*, and vw* are voltage command values on the stationary coordinates,and include a U-phase voltage command value vu*, a V-phase voltagecommand value vv*, and a W-phase voltage command value vw*.

A well-known technology can be applied to the voltage application unit1. Therefore, a detailed description is omitted. However, for example,the voltage application unit 1 includes a plurality of semiconductorswitches capable of on/off control, and is configured to use thethree-phase voltage command values vu*, vv*, and vw* to apply the on/offcontrol to the respective semiconductor switches, to thereby generatethree-phase AC voltages vu, vv, and vw.

When the voltage application unit 1 applies the three-phase AC voltagesvu, vv, and vw to the AC rotating machine 2, relative differences inelectric potential among the three-phase AC voltages vu, vv, and vw areonly required to substantially match relative differences in electricpotential among the three-phase voltage command values vu*, vv*, andvw*. Therefore, voltage values for increasing a voltage utilizationfactor may be added to the three-phase voltage command values vu*, vv*,and vw*. Moreover, correction voltage values resulting from on-voltagevalues or dead times of the respective semiconductor switches may beadded to the respective three-phase voltage command values vu*, vv*, andvw*.

The AC rotating machine 2 is more specifically a permanent magnet typesynchronous motor, such as a surface magnet type synchronous motor or anembedded magnet type synchronous motor. The AC rotating machine 2 maybe, for example, a reluctance synchronous motor, which does not use amagnet for a rotor, or a field winding type synchronous motor, which hasa field winding circuit on the secondary side.

The position detection unit 3 is configured to detect a rotationposition θ of the AC rotating machine 2. A well-known technology can beapplied also to the position detection unit 3. Therefore, although adetailed description is omitted, the position detection unit 3 includes,for example, a resolver, which is a rotation angle sensor coupled to arotation shaft of the AC rotating machine 2, and is configured togenerate a signal in accordance with the rotation position θ, which isan angle of a rotor of the AC rotating machine 2. The signal inaccordance with the rotation position θ is output as a digital signalindicating the rotation position θ by the R/D converter incorporated inthe position detection unit 3. A Hall element, a magnetoresistiveelement, or the like may be employed in place of the R/D converter. Therotation position θ may be estimated based on a well-known technology.

A well-known technology can also be applied to the current detectionunit 4. Therefore, although a detailed description is omitted, forexample, the current detection unit 4 is coupled to the three-phasepower supply lines 11, and is configured to detect three-phase ACcurrents flowing through the AC rotating machine 2 based on thethree-phase AC voltages vu, vv, and vw, to output three-phase detectioncurrents iu, iv, and iw, which are detection results, as digitalsignals. Therefore, the current detection unit 4 includes, for example,a current sensor and an A/D converter for each phase.

Moreover, the current detection unit 4 includes a calculation unitconfigured to estimate, when there is a phase having an undetectable ACcurrent, the value of the AC current in the phase having theundetectable current based on calculation. This calculation unit isconfigured to calculate, for example, based on a fact that a sum of thethree-phase detection currents iu, iv, and iw is zero, the current inthe phase unavailable for the detection from the currents in the twophases available for the detection. Alternatively, the calculation unitmay be configured to use the current detected in the past in the phaseunavailable for the detection and the rotation position θ to calculatethe current in this phase (for example, see Patent Literature 2).

In the first embodiment, the current detection unit 4 is configured todetect the three-phase AC currents from the three-phase power supplylines 11 connecting the voltage application unit 1 and the AC rotatingmachine 2 to each other, but the current detection unit 4 may beconfigured to detect the three-phase AC currents from a locationdifferent from the three-phase power supply lines 11. For example, thecurrent detection unit 4 may be configured to detect bus currents insidethe voltage application unit 1, to thereby output the detected buscurrents as the three-phase detection currents iu, iv, and iw.

The current detection unit 4 is configured to output the three-phasedetection currents iu, iv, and iw at each first operation timingrepeated at freely-set predetermined cycles ΔT1. As a result, thethree-phase detection currents iu, iv, and iw are updated at each firstoperation timing. The updated three-phase detection currents iu, iv, andiw are held until the arrival of the next first operation timing. Thecycle ΔT1 of the first operation timing is hereinafter referred to as“first operation cycle ΔT1.” This first operation cycle ΔT1 is thedetection cycle for detecting the currents, is also a calculation cyclefor executing the calculation, and is set to, for example, 100×10⁻⁶(seconds) to 500×10⁻⁶ (seconds). The three-phase detection currents iu,iv, and iw are detection currents on the stationary coordinates, andinclude a U-phase detection current iu, a V-phase detection current iv,and a W-phase detection current iw.

The position detection unit 3 is configured to output the rotationposition θ at each first operation timing repeated at the firstoperation cycles ΔT1. The rotation position θ is updated at each firstoperation timing. The updated rotation position θ is held until thearrival of the next first operation timing. The rotation position θ is aposition signal on the stationary coordinates, and is output to thefirst coordinate conversion unit 6 and the second coordinate conversionunit 8.

The first coordinate conversion unit 6 is configured to apply coordinateconversion to the three-phase detection currents iu, iv, and iw based onany phase, to thereby output two-phase detection currents id and iq. Inthe first embodiment, the rotation position θ output from the positiondetection unit 3 is used as the any phase used for the coordinateconversion. A phase different from the rotation position θ may beemployed as the any phase. For example, the any phase may be a phase ofany one of the phases of the currents supplied to the AC rotatingmachine 2 or the voltages applied to the AC rotating machine 2.

The first coordinate conversion unit 6 is configured to convert thethree-phase detection currents iu, iv, and iw from the current detectionunit 4 to the two-phase detection currents id and iq based on therotation position θ output from the position detection unit 3. The firstcoordinate conversion unit 6 is configured to output the two-phasedetection currents id and iq at each first operation timing repeated atthe first operation cycles ΔT1. The two-phase detection currents id andiq are updated at each first operation timing. The updated two-phasedetection currents id and iq are held until the arrival of the nextfirst operation timing. The two-phase detection currents id and iq aredigital signals of the detection currents on the rotational coordinates,and include a d-axis component id on a d axis and a q-axis component iqon a q axis, which are orthogonal to each other.

The current control unit 7 is configured to input two-phase currentcommand values id* and iq* on the rotational coordinates from theoutside, and to input the two-phase detection currents id and iq on therotational coordinates from the first coordinate conversion unit 6. Thetwo-phase current command values id* and iq* are digital signals ofcurrent command values on the rotational coordinates indicating currentsto be supplied to the AC rotating machine 2, and include a d-axiscomponent id* on the d axis and a q-axis component iq* on the q axis,which are orthogonal to each other. The two-phase detection currents idand iq are supplied from the first coordinate conversion unit 6 to thecurrent control unit 7. The current control unit 7 is configured tooutput digital two-phase voltage command values vd1* and vq1* on therotational coordinates based on those two-phase current command valuesid* and iq′ on the rotational coordinates and the two-phase detectioncurrents id and iq on the rotational coordinates. The two-phase voltagecommand values vd1* and vq1* include a d-axis component vd1* on the daxis and a q-axis component vq1* on the q axis, which are orthogonal toeach other.

The current control unit 7 is configured to output the two-phase voltagecommand values vd1* and vq1* at each first operation timing repeated atthe first operation cycles ΔT1. In other words, the two-phase voltagecommand values vd1* and vq1* are updated at each first operation timingrepeated at the first operation cycles ΔT1. The updated two-phasevoltage command values vd1* and vq1* are held until the arrival of thenext first operation timing.

The second coordinate conversion unit 8 is configured to applycoordinate conversion to the two-phase voltage command values vd1* andvq1* on the rotational coordinates input from the current control unit 7based on the rotation position θ output from the position detection unit3, to thereby output first three-phase voltage command values vu1*,vv1*, and vw1*. Those first three-phase voltage command values vu1*,vv1*, and vw1* are digital signals of voltage command values on thestationary coordinates, and include a first U-phase voltage commandvalue vu1*, a first V-phase voltage command value vv1*, and a firstW-phase voltage command value vw1*. Those first three-phase voltagecommand values vu1*, vv1*, and vw1* are supplied to the voltage commandgeneration unit 9 and the voltage command output unit 10.

The updated rotation position θ is input to the second coordinateconversion unit 8 at each first operation timing repeated at the firstoperation cycles ΔT1. The second coordinate conversion unit 8 isconfigured to output the first three-phase voltage command values vu1*,vv1*, and vw1* obtained based on the updated rotation position θ at eachfirst operation timing. As a result, the first three-phase voltagecommand values vu1*, vv1*, and vw1* are updated at each first operationtiming repeated at the first operation cycles ΔT1. The updated firstthree-phase voltage command values vu1*, vv1*, and vw1* are held untilthe arrival of the next first operation timing.

The angular frequency calculation unit 60 is configured to input therotation position θ from the position detection unit 3, and to calculatean angular frequency ω, which is a change rate of the input rotationposition θ. For this purpose, the angular frequency calculation unit 60includes a delay-and-hold operator 61, a subtractor 62, and aproportional gain multiplier 63.

In the angular frequency calculation unit 60, the rotation position θoutput by the position detection unit 3 is input to the delay-and-holdoperator 61. The delay-and-hold operator 61 is configured to delay theinput by a delay time interval ΔTd, and to then hold the delayed input.The delay time interval ΔTd is, for example, a period having the samelength as that of the first operation cycle ΔT1. The subtractor 62 isconfigured to input the rotation position θ from the position detectionunit 3 and the rotation position θ delayed by the delay-and-holdoperator 61, to subtract the rotation position θ that is the delay timeinterval ΔTd earlier than the current rotation position θ, and to outputa subtraction result to the proportional gain multiplier 63.

The proportional gain multiplier 63 is configured to multiply the outputof the subtractor 62 by (1/ΔTd), to thereby obtain a change in rotationposition θ per unit time to output the obtained change as the angularfrequency ω, which is the change rate of the rotation position θ. Theangular frequency co is output as a digital signal to the voltagecommand generation unit 9. In the first embodiment, the delay timeinterval ΔTd is set as the first operation cycle ΔT1 as described aboveso that the angular frequency calculation unit 60 outputs the angularfrequency ω at each first operation timing repeated at the firstoperation cycles ΔT1.

The voltage command generation unit 9 is configured to generate secondthree-phase voltage command values vu2*, vv2*, and vw2* based on thefirst three-phase voltage command values vu1*, vv1*, and vw1* from thesecond coordinate conversion unit and the angular frequency ω from theangular frequency calculation unit 60.

The voltage command output unit 10 is configured to input the firstthree-phase voltage command values vu1*, vv1*, and vw1* supplied fromthe second coordinate conversion unit 8 and the second three-phasevoltage command values vu2*, vv2*, and vw2* supplied from the voltagecommand generation unit 9, to select any one of the two groups ofcommand values, and to output the selected one group of command valuesas the three-phase voltage command values vu*, vv*, and vw* to thevoltage application unit 1. In this case, an operation cycle forselecting the first three-phase voltage command values vu1*, vv1*, andvw1* and an operation cycle for selecting the second three-phase voltagecommand values vu2*, vv2*, and vw2* are different from each other. Morespecifically, the voltage command output unit 10 is configured to selectthe first three-phase voltage command values vu1*, vv1*, and vw1* outputfrom the second coordinate conversion unit 8 correspondingly to eachfirst operation timing repeated at the first operation cycles ΔT1.Moreover, the voltage command output unit 10 is configured to select thesecond three-phase voltage command values vu2*, vv2*, and vw2* outputfrom the voltage command generation unit 9 correspondingly to eachsecond operation timing repeated at second operation cycles ΔT2. As aresult, the three-phase voltage command values vu*, vv*, and vw* arealways continuously output to the voltage application unit 1.

This second operation cycle ΔT2 is set shorter than the first operationcycle ΔT1. This second operation cycle ΔT2 is practically set to, forexample, ½ time to 1/20 times the first operation cycle ΔT1. However,the second operation cycle ΔT2 is only required to be shorter than thefirst operation cycle ΔT1, and is not limited to this practical range.Moreover, it is preferred that the second operation cycle ΔT2 be set to1/n time (n: integer) the first operation cycle ΔT1, but the setting isnot limited to this example. As a result of setting the second operationcycle ΔT2 shorter than the first operation cycle ΔT1, one or more secondoperation timings exist between the two first operation timings next toeach other.

When the first operation timing and the second operation timing matcheach other, in the first embodiment, the first operation timing isprioritized, and is treated in such a manner that only the firstoperation timing is reached. That is, only the processing at the firstoperation timing is executed, and the processing at the second operationtiming is not executed.

Moreover, when one second operation timing is set to exist between thetwo first operation timings next to each other, the first operationcycle ΔT1 and the second operation cycle £T2 may be the same cycles, andthe first operation timing and the second operation timing may bedifferent timings. In view of this fact, synchronization between thefirst operation timing and the second operation timing is not alwaysrequired.

The voltage command output unit 10 includes a U-phase switch su, aV-phase switch sv, and a W-phase switch sw in order to select any one ofthe first three-phase voltage command values vu1*, vv1*, and vw1* andthe second three-phase voltage command values vu2*, vv2*, and vw2*. Thefirst U-phase voltage command value vu1* and the second U-phase voltagecommand value vu2* are input to the U-phase switch su. This U-phaseswitch su is configured to output any one of the first U-phase voltagecommand value vu1* and the second U-phase voltage command value vu2* asthe U-phase voltage command value vu*.

The first V-phase voltage command value vv1* and the second V-phasevoltage command value vv2* are input to the V-phase switch sv. ThisV-phase switch sv is configured to output any one of the first V-phasevoltage command value vv1* and the second V-phase voltage command valuevv2* as the V-phase voltage command value vv*. The first W-phase voltagecommand value vw1* and the second W-phase voltage command value vw2* areinput to the W-phase switch sw. This W-phase switch sw is configured tooutput any one of the first W-phase voltage command value vw1* and thesecond W-phase voltage command value vw2* as the W-phase voltage commandvalue vw*.

The switches su, sv, and sw are operationally associated with oneanother. Therefore, for example, when the U-phase switch su selects thefirst U-phase voltage command value vu1*, the V-phase switch sv selectsthe first V-phase voltage command value vv1*, and the W-phase switch swselects the first W-phase voltage command value vw1*. Similarly, forexample, when the U-phase switch su selects the second U-phase voltagecommand value vu2*, the V-phase switch sv selects the second V-phasevoltage command value vv2*, and the W-phase switch sw selects the secondW-phase voltage command value vw2*. Those selection results are helduntil the first operation timing or the second operation timing arrivesnext.

The voltage command output unit 10 further includes a switch flag outputunit 10 sf. This switch flag output unit 10 sf is configured to output aswitch flag FLG_SW, which is a signal, to the voltage command generationunit 9 in accordance with the selection state of the voltage commandoutput unit 10. This switch flag FLG_SW is switched between, forexample, “TRUE” and “FALSE”. For example, the switch flag output unit 10sf sets the switch flag FLG_SW to “TRUE” under the state in which thefirst three-phase voltage command values vu1*, vv1*, and vw1* areselected, and sets the switch flag FLG_SW to “FALSE” under the state inwhich the second three-phase voltage command values vu2*, vv2*, and vw2*are selected.

The voltage command generation unit 9 specifically includes a storageunit 90 and a voltage command calculation unit 91. The first three-phasevoltage command values vu1*, vv1*, and vw1* from the second coordinateconversion unit 8 and the switch flag FLG_SW from the voltage commandoutput unit 10 are input to the storage unit 90.

As described above, the switch flag FLG_SW becomes “TRUE”correspondingly to each first operation timing repeated at the firstoperation cycles ΔT1. When the switch flag FLG_SW becomes “TRUE”, thestorage unit 90 stores the first three-phase voltage command valuesvu1*, vv1*, and vw1* output from the second coordinate conversion unit8. As a result, the first three-phase voltage command values vu1*, vv1*,and vw1* generated by the second coordinate conversion unit 8 at eachfirst operation cycle ΔT1 are stored in the storage unit 90.

As described above, the switch flag FLG_SW becomes “FALSE”correspondingly to each second operation timing repeated at the secondoperation cycles ΔT2. One or more second operation timings exist betweenthe two first operation timings next to each other. When the switch flagFLG_SW becomes “FALSE”, the storage unit 90 outputs the firstthree-phase voltage command values vu1*, vv1*, and vw1* stored at thefirst operation timing immediately before the current first operationtiming as three-phase memory voltage command values vu1h*, vv1h*, andvw1h*. The three-phase memory voltage command values vu1h*, vv1h*, andvw1h* are digital signals of the voltage command values on thestationary coordinates, and include a U-phase memory voltage commandvalue vu1h*, a V-phase memory voltage command value vv1h*, and a W-phasememory voltage command value vw1h*.

The three-phase memory voltage command values vu1h*, vv1h*, and vw1h*from the storage unit 90 and the angular frequency ω from the angularfrequency calculation unit 60 are output to the voltage commandcalculation unit 91. The voltage command calculation unit 91 isconfigured to correct phases of the three-phase memory voltage commandvalues vu1h*, vv1h*, and vw1h* based on the angular frequency ω, tooutput the three-phase memory voltage command values vu1h*, vv1h*, andvw1h* after the correction as the second three-phase voltage commandvalues vu2*, vv2*, and vw2* at each second operation timing. As aresult, the second three-phase voltage command values vu2*, vv2*, andvw2* are updated at each second operation timing. The updated secondthree-phase voltage command values vu2*, vv2*, and vw2* are held untilthe second operation timing arrives next. The second three-phase voltagecommand values vu2*, vv2*, and vw2* are output to the voltage commandoutput unit 10. The second three-phase voltage command values vu2*,vv2*, and vw2* are digital signals of voltage command values on thestationary coordinates, and include the second U-phase voltage commandvalue vu2*, the second V-phase voltage command value vv2*, and thesecond W-phase voltage command value vw2*.

FIG. 2 is a block diagram for illustrating an internal configurationexample of the current control unit 7 employed in the control device foran AC rotating machine according to the first embodiment of the presentinvention. As illustrated in FIG. 2, this current control unit 7includes subtractors 20 and 26, proportional gain multipliers 21 and 27,integral gain multipliers 22 and 28, adders 23 and 29, delay-and-holdoperators 24 and 30, and adders 25 and 31.

The subtractor 20 is configured to subtract the d-axis component id ofthe two-phase detection currents id and iq on the rotational coordinatesfrom the d-axis component id* of the two-phase current command valuesid* and iq* on the rotational coordinates, to output a d-axis currentdifference (id*−id) to the proportional gain multiplier 21 and theintegral gain multiplier 22. The proportional gain multiplier 21 isconfigured to multiply the d-axis current difference (id*−id) by, forexample, a proportional gain kp, which is a fixed value, to therebyoutput the product. The integral gain multiplier 22 is configured tomultiply the d-axis current difference (id*−id) by an integral gainkiΔT1, to thereby output the product. The adder 23 is configured to addthe output of the integral gain multiplier 22 and an output of thedelay-and-hold operator 24 to each other, to thereby output the sum tothe delay-and-hold operator 24. The delay-and-hold operator 24 isconfigured to delay the input by a delay time interval corresponding tothe first operation cycle ΔT1, and holds the output of the adder 23.

As described above, the result kiΔT1 (id*−id) of the multiplication bythe integral gain multiplier 22 and the output of the delay-and-holdoperator 24 are added to each other by the adder 23. A result of theaddition is delayed by the delay time interval corresponding to thefirst operation cycle ΔT1, and is newly held by the delay-and-holdoperator 24 after that. Therefore, the adder 23 is configured to add theoutput of the integral gain multiplier 22 and the output of thedelay-and-hold operator 24 to each other, to thereby output the d-axiscomponent vd1* of the two-phase voltage command values vd1* and vq1* onthe rotational coordinates. This d-axis component vd1*, namely, theresult of the addition of components of change simulated by each of theproportional gain kp and the integral gain kiΔT1 to the d-axis currentdifference (id*−id), corresponds to a result of proportional integral ofthe d-axis current difference (id*−id) output by the subtractor 20. Thedelay-and-hold operator 24 holds the d-axis component vd1*.

Similarly, the subtractor 26 is configured to subtract the q-axiscomponent iq of the two-phase detection currents id and iq on therotational coordinates from the q-axis component iq* of the two-phasecurrent command values id* and iq* on the rotational coordinates, tooutput a q-axis current difference (iq*−iq) to the proportional gainmultiplier 27 and the integral gain multiplier 28. The proportional gainmultiplier 27 is configured to multiply the q-axis current difference(iq*−iq) by a proportional gain kp, to thereby output the product. Theintegral gain multiplier 28 is configured to multiply the q-axis currentdifference (iq*−iq) by an integral gain kiΔT1, to thereby output theproduct. The adder 29 is configured to add the output of the integralgain multiplier 28 and an output of the delay-and-hold operator 30 toeach other, to thereby output the sum to the delay-and-hold operator 30.The delay-and-hold operator 30 is configured to delay the input by adelay time interval corresponding to the first operation cycle ΔT1, andholds the output.

As described above, the result kiΔT1(iq*−iq) of the multiplication bythe integral gain multiplier 28 and the output of the delay-and-holdoperator 30 are added to each other by the adder 29. A result of theaddition is delayed by the delay time interval corresponding to thefirst operation cycle ΔT1, and is newly held by the delay-and-holdoperator 30 after that. Therefore, the adder 29 is configured to add theoutput of the integral gain multiplier 28 and the output of thedelay-and-hold operator 30 to each other, to thereby output the q-axiscomponent vq1* of the two-phase voltage command values vd1* and vq1* onthe rotational coordinates. This q-axis component vq1*, namely, theresult of the addition of components of change simulated by each of theproportional gain kp and the integral gain kiΔT1 to the q-axis currentdifference (iq*−iq), corresponds to a result of proportional integral ofthe q-axis current difference (iq*−iq) output by the subtractor 26. Thedelay-and-hold operator 30 holds the q-axis component vq1*.

FIG. 3 is a block diagram for illustrating a configuration example ofthe storage unit 90 of the voltage command generation unit 9 mounted inthe control device for an AC rotating machine according to the firstembodiment of the present invention. As illustrated in FIG. 3, thestorage unit 90 includes sample-and-hold devices 40 to 42 for therespective phases. The sample-and-hold devices 40 to 42 are eachcontrolled in accordance with the switch flag FLG_SW output from theswitch flag output unit 10 sf of the voltage command output unit 10.

The sample-and-hold device 40 is configured to sample and hold the firstU-phase voltage command value vu1* when the switch flag FLG_SW becomes“TRUE”, to thereby store and hold this first U-phase voltage commandvalue vu1* as the U-phase memory voltage command value vu1h*. Thissample-and-hold device 40 is configured to output the stored and heldU-phase memory voltage command value vu1h* when the switch flag FLG_SWbecomes “FALSE”.

Similarly, the sample-and-hold device 41 is configured to sample andhold the first V-phase voltage command value vv1* when the switch flagFLG_SW becomes “TRUE”, to thereby store and hold this first V-phasevoltage command value vv1* as the V-phase memory voltage command valuevv1h*. This sample-and-hold device 41 is configured to output the storedand held V-phase memory voltage command value vv1h* when the switch flagFLG_SW becomes “FALSE”.

Similarly, the sample-and-hold device 42 is configured to sample andhold the first W-phase voltage command value vw1* when the switch flagFLG_SW becomes “TRUE”, to thereby store and hold this first W-phasevoltage command value vw1* as the W-phase memory voltage command valuevw1h*. This sample-and-hold device 42 is configured to output the storedand held W-phase memory voltage command value vw1h* when the switch flagFLG_SW becomes “FALSE”.

Before description of an operation of the voltage command calculationunit 91, description is now given of a principle of phase correction.FIG. 4 is an explanatory graph for showing the principle of the phasecorrection executed in the voltage command calculation unit 91. A state“x” of a rotation at an angular frequency ω is plotted. In thisrepresentation, for the sake of convenience, stationary two-axiscoordinates (α axis and β axis, obtained by well-knownthree-phase/two-phase conversion are used as the stationary coordinatesin place of the three-phase coordinates, and the state “x” is plotted onthose stationary two-phase coordinates. In this representation, theangular frequency ω may be the angular frequency ω output by the angularfrequency calculation unit 60, but may be different from that angularfrequency ω. Moreover, a very short period ΔT may also be different froma reference operation cycle ΔT described below.

An α-axis component in the state “x” at a certain time point isindicated as x_(α)(n). A β-axis component is indicated as x_(β)(n).Moreover, when the very short period ΔT elapses from the certain timepoint, the a-axis component in the state “x” is indicated as x_(α)(n+1),and the β-axis component is indicated as x_(β)(n+1). The state “x” isrotating at the angular frequency ω, and a relationship given byExpression (1) below is satisfied between x_(α)(n) and x_(β)(n), andx_(α)(n+1) and x_(β)(n+1).

$\begin{matrix}{\begin{pmatrix}{x_{\alpha}\left( {n + 1} \right)} \\{x_{\beta}\left( {n + 1} \right)}\end{pmatrix} = {\begin{pmatrix}{\cos\left( {{\omega\Delta}\; T} \right)} & {- {\sin\left( {{\omega\Delta}\; T} \right)}} \\{\sin\left( {{\omega\Delta}\; T} \right)} & {\cos\left( {{\omega\Delta}\; T} \right)}\end{pmatrix}\begin{pmatrix}{x_{\alpha}(n)} \\{x_{\beta}(n)}\end{pmatrix}}} & (1)\end{matrix}$

When it is also assumed that ωΔT is also very small, approximationsgiven by Expression (2) and Expression (3) below are satisfied.cos(ωΔT)≈1  (2)sin(ωΔT)≈ωΔT   (3)

Expression (4) below is obtained by assigning Expression (2) andExpression (3) to Expression (1).

$\begin{matrix}{\begin{pmatrix}{x_{\alpha}\left( {n + 1} \right)} \\{x_{\beta}\left( {n + 1} \right)}\end{pmatrix} = {\begin{pmatrix}1 & {{- {\omega\Delta}}\; T} \\{{\omega\Delta}\; T} & 1\end{pmatrix}\begin{pmatrix}{x_{\alpha}(n)} \\{x_{\beta}(n)}\end{pmatrix}}} & (4)\end{matrix}$

Expression (4) corresponds to a change in the state “x” rotating at theangular frequency ω represented on the stationary two-axis coordinates(α axis and β axis) when the very short period ΔT elapses. The state “x”on the stationary three-phase coordinates is given by Expression (5)below based on Expression (1) and Expression (4).

$\begin{matrix}{\begin{matrix}{\begin{pmatrix}{x_{u}\left( {n + 1} \right)} \\{x_{v}\left( {n + 1} \right)} \\{x_{w}\left( {n + 1} \right)}\end{pmatrix} = {\left( {\sqrt{\frac{2}{3}}\begin{pmatrix}1 & 0 \\{- \frac{1}{2}} & \frac{\sqrt{3}}{2} \\{- \frac{1}{2}} & {- \frac{\sqrt{3}}{2}}\end{pmatrix}} \right)\begin{pmatrix}{\cos\left( {{\omega\Delta}\; T} \right)} & {- {\sin\left( {{\omega\Delta}\; T} \right)}} \\{\sin\left( {{\omega\Delta}\; T} \right)} & {\cos\left( {{\omega\Delta}\; T} \right)}\end{pmatrix}}} \\{\left( {\sqrt{\frac{2}{3}}\begin{pmatrix}1 & {- \frac{1}{2}} & {- \frac{1}{2}} \\0 & \frac{\sqrt{3}}{2} & {- \frac{\sqrt{3}}{2}}\end{pmatrix}} \right)\begin{pmatrix}{x_{u}(n)} \\{x_{v}(n)} \\{x_{w}(n)}\end{pmatrix}} \\{= {\left( {\sqrt{\frac{2}{3}}\begin{pmatrix}1 & 0 \\{- \frac{1}{2}} & \frac{\sqrt{3}}{2} \\{- \frac{1}{2}} & {- \frac{\sqrt{3}}{2}}\end{pmatrix}} \right)\begin{pmatrix}1 & {{- {\omega\Delta}}\; T} \\{{\omega\Delta}\; T} & 1\end{pmatrix}}} \\{\left( {\sqrt{\frac{2}{3}}\begin{pmatrix}1 & {- \frac{1}{2}} & {- \frac{1}{2}} \\0 & \frac{\sqrt{3}}{2} & {- \frac{\sqrt{3}}{2}}\end{pmatrix}} \right)\begin{pmatrix}{x_{u}(n)} \\{x_{v}(n)} \\{x_{w}(n)}\end{pmatrix}} \\{= \begin{pmatrix}\frac{2}{3} & {- \frac{1 + {\sqrt{3}{\omega\Delta}\; T}}{3}} & {- \frac{1 - {\sqrt{3}{\omega\Delta}\; T}}{3}} \\{- \frac{1 - {\sqrt{3}{\omega\Delta}\; T}}{3}} & \frac{2}{3} & {- \frac{1 + {\sqrt{3}{\omega\Delta}\; T}}{3}} \\{- \frac{1 + {\sqrt{3}{\omega\Delta}\; T}}{3}} & {- \frac{1 - {\sqrt{3}{\omega\Delta}\; T}}{3}} & \frac{2}{3}\end{pmatrix}}\end{matrix}\quad} & (5)\end{matrix}$

Expression (5) can be transformed to Expression (6) below inconsideration of a relationship of xu(n)+xv(n)+xw(n)=0.

$\begin{matrix}{\begin{matrix}{\begin{pmatrix}{x_{u}\left( {n + 1} \right)} \\{x_{v}\left( {n + 1} \right)} \\{x_{w}\left( {n + 1} \right)}\end{pmatrix} = \begin{pmatrix}\frac{2}{3} & {- \frac{1 + {\sqrt{3}{\omega\Delta}\; T}}{3}} & {- \frac{1 - {\sqrt{3}{\omega\Delta}\; T}}{3}} \\{- \frac{1 - {\sqrt{3}{\omega\Delta}\; T}}{3}} & \frac{2}{3} & {- \frac{1 + {\sqrt{3}{\omega\Delta}\; T}}{3}} \\{- \frac{1 + {\sqrt{3}{\omega\Delta}\; T}}{3}} & {- \frac{1 - {\sqrt{3}{\omega\Delta}\; T}}{3}} & \frac{2}{3}\end{pmatrix}} \\{\begin{pmatrix}{x_{u}(n)} \\{x_{v}(n)} \\{x_{w}(n)}\end{pmatrix} +} \\{\frac{1}{3}\begin{pmatrix}1 & 1 & 1 \\1 & 1 & 1 \\1 & 1 & 1\end{pmatrix}\begin{pmatrix}{x_{u}(n)} \\{x_{v}(n)} \\{x_{w}(n)}\end{pmatrix}} \\{= {\begin{pmatrix}1 & {- \frac{{\omega\Delta}\; T}{3}} & \frac{{\omega\Delta}\; T}{3} \\\frac{{\omega\Delta}\; T}{3} & 1 & {- \frac{{\omega\Delta}\; T}{3}} \\{- \frac{{\omega\Delta}\; T}{3}} & \frac{{\omega\Delta}\; T}{3} & 1\end{pmatrix}\begin{pmatrix}{x_{u}(n)} \\{x_{v}(n)} \\{x_{w}(n)}\end{pmatrix}}}\end{matrix}\quad} & (6)\end{matrix}$

As described above, x(n+1) at the time when the very short period ΔTelapses can be obtained based on the state x(n) rotating at the angularfrequency ω on the stationary three-phase coordinates as given byExpression (5) or Expression (6).

A calculation amount is smaller in the case of Expression (5) than inthe case of Expression (6) when the angular frequency ω is given.Therefore, the voltage command calculation unit 91 in the firstembodiment is configured to correct the respective phases of thethree-phase memory voltage command values vu1h*, vv1h*, and vw1h* on thestationary coordinates output by the storage unit 90 based on Expression(6), to output the three-phase memory voltage command values vu1h*,vv1h*, and vw1h* after the correction as the second three-phase voltagecommand values vu2*, vv2*, and vw2* on the stationary coordinates.

The approximation given by Expression (4) is used in the firstembodiment, but Expression (5), which is the calculation expression forthe phase correction, may be used in place of Expression (4) for theapproximation. Similarly, the approximation given by Expression (2) maybe replaced by, for example, the approximation of “cos(ωΔT)≈1−(ωΔT)²÷2”based on the Maclaurin's expansion, to thereby derive an expression forthe phase correction.

FIG. 5 is a block diagram for illustrating a configuration example ofthe voltage command calculation unit 91 included in the voltage commandgeneration unit 9 mounted in the control device for an AC rotatingmachine according to the first embodiment of the present invention. Asillustrated in FIG. 5, the voltage command calculation unit 91 includesa proportional gain multiplier 70, multipliers 71, 72, and 73,subtractors 74, 77, and 78, and adders 75, 76, and 79.

In FIG. 5, the proportional gain multiplier 70 is configured to multiplythe angular frequency ω output from the angular frequency calculationunit 60 by, for example, (ΔT/(3)^(1/2)), which is a fixed valuepredetermined as a proportional gain, to thereby output a result(ωΔT/(3)^(1/2)) of this multiplication. The multiplier 71 is configuredto multiply the U-phase memory voltage command value vu1h* on thestationary coordinates by the multiplication result (ωΔT/(3)^(1/2))output by the proportional gain multiplier 70, to thereby output aresult {(ωΔT/(3)^(1/2))vu1h*} of the multiplication. The multiplier 72is configured to multiply the V-phase memory voltage command value vv1h*on the stationary coordinates by the multiplication result(ωΔT/(3)^(1/2)) output by the proportional gain multiplier 70, tothereby output a result {(ωΔT/(3)^(1/2))vv1h*} of the multiplication.The multiplier 73 is configured to multiply the W-phase memory voltagecommand value vw1h* on the stationary coordinates by the multiplicationresult (ωΔT/(3)^(1/2)) output by the proportional gain multiplier 70, tothereby output a result {(ωΔT/(3)^(1/2))vw1h*} of the multiplication.

The subtractor 74 is configured to subtract the multiplication result{(ωΔT/(3)^(1/2))vv1h*} output by the multiplier 72 from the U-phasememory voltage command value vu1h* on the stationary coordinates, tothereby output the subtraction result {vu1h*−(ωΔT/(3)^(1/2))vv1h*}. Theadder 75 is configured to add the multiplication result{(ωΔT/(3)^(1/2))vw1h*} output by the multiplier 73 to the subtractionresult {vu1h*−(ωΔT/(3)^(1/2))vv1h*} output by the subtractor 74, tothereby output a result of the addition[{vu1h*−(ωΔT/(3)^(1/2))vv1h*}+{(ωΔT/(3)^(1/2))vw1h*}].

When it is assumed that the memory voltage command values vu1h*, vv1h*,and vw1h* in the U, V, and W phases on the stationary coordinates are inthe state x(n) given by Expression (6), the output[{vu1h*−(ωΔT/(3)^(1/2))vv1h*}+{(ωΔT/(3)^(1/2))vw1h*}] of the adder 75has content corresponding to the first row on the right side ofExpression (6), and becomes the second U-phase voltage command valuevu2* on the stationary coordinates.

Similarly, the adder 76 is configured to add the multiplication result{(ωΔT/(3)^(1/2))vu1h*} output by the multiplier 71 to the V-phase memoryvoltage command value vv1h* on the stationary coordinates, to therebyoutput the addition result {vv1h*+(ωΔT/(3)^(1/2))vu1h*}. The subtractor77 is configured to subtract the multiplication result{(wΔT/(3)^(1/2))vw1h*} output by the multiplier 73 from the additionresult {vv1h*+(ωΔT/(3)^(1/2))vu1h*} output by the adder 76, to therebyoutput a result of the subtraction[{vv1h*+(ωΔT/(3)^(1/2))vu1h*}−{(ωΔT/(3)^(1/2))vw1h*)}].

When it is assumed that the memory voltage command values vu1h*, vv1h*,and vw1h* in the U, V, and W phases on the stationary coordinates are inthe state x(n) given by Expression (6), the output[{vv1h*+(ωΔT/(3)^(1/2))vu1h*}−{(ωΔT/(3)^(1/2))vw1h*}] of the subtractor77 has content corresponding to the second row on the right side ofExpression (6), that is, the second V-phase voltage command value vv2*on the stationary coordinates.

Similarly, the subtractor 78 is configured to subtract themultiplication result {(ωΔT/(3)^(1/2))vu1h*} output by the multiplier 71from the W-phase memory voltage command value vw1h* on the stationarycoordinates, to thereby output the subtraction result{vw1h*−(ωΔT/(3)^(1/2))vu1h*}. The adder 79 is configured to add themultiplication result {(ωΔT/(3)^(1/2))vv1h*} output by the multiplier 72to the subtraction result {vw1h*−(ωΔT/(3)^(1/2))vu1h*} output by thesubtractor 78, to thereby output a result of the addition[{vw1h*−(ωΔT/(3)^(1/2))vu1h*}+{(ωΔT/(3)^(1/2))vv1h*}].

A second three-phase voltage command value in any one phase of thesecond three-phase voltage command values vu2*, vv2*, and vw2* on thestationary coordinates may be calculated from those values in remainingtwo phases based on a relationship that a sum of the second three-phasevoltage command values vu2*, vv2*, and vw2* on the stationarycoordinates is zero.

When it is assumed that the memory voltage command values vu1h*, vv1h*,and vw1h* in the U, V, and W phases on the stationary coordinates are inthe state x(n) given by Expression (6), the output[{vw1h*−(ωΔT/(3)^(1/2))vu1h*}+{(ωΔT/(3)^(1/2))vv1h*}] of the adder 79has content corresponding to the third row on the right side ofExpression (6), that is, the second W-phase voltage command value vw2*on the stationary coordinates.

When the voltage command output unit 10 selects the first three-phasevoltage command values vu1*, vv1*, and vw1* as the three-phase voltagecommand values vu*, vv*, and vw* on the stationary coordinates, thecalculation result of the voltage command calculation unit 91 is notreflected to any units. Therefore, when the voltage command output unit10 selects the first three-phase voltage command values vu1*, vv1*, andvw1*, the execution of the calculation in the voltage commandcalculation unit 91 can be omitted.

Similarly, when the voltage command output unit 10 selects the secondthree-phase voltage command values vu2*, vv2*, and vw2* as thethree-phase voltage command values vu*, vv*, and vw* on the stationarycoordinates, the respective calculation results of the current detectionunit 4, the first coordinate conversion unit 6, the current control unit7, and the second coordinate conversion unit 8 are not reflected to anyunits. Therefore, the execution of the calculations in the currentdetection unit 4, the first coordinate conversion unit 6, the currentcontrol unit 7, and the second coordinate conversion unit 8 can beomitted.

FIG. 6 is an example of a time chart for showing operation examples ofthe respective units in the control device for an AC rotating machineaccording to the first embodiment of the present invention. This timechart is a time chart in a case in which the second operation cycle ΔT2is set to ½ time the first operation cycle ΔT1. In this case, it isassumed that the first operation cycle ΔT1 and the second operationcycle ΔT2 are generated from the reference operation cycle ΔT serving asa reference timing of the operation, and the second operation cycle ΔT2is set to the reference operation cycle ΔT. On the basis of thisassumption, the second operation timing arrives twice while the firstoperation timing arrives each time the first operation cycle ΔT1elapses. One of the two times of the second operation timings arrives atthe same timing as the first operation timing.

In FIG. 6, time points (seconds) having the reference operation cycle ΔTas a unit are shown as 0, ΔT, 2ΔT, . . . , 7ΔT on a row (a). On a row(b) to a row (j), operation states at each time point of the positiondetection unit 3, the current detection unit 4, the first coordinateconversion unit 6, the current control unit 7, the second coordinateconversion unit 8, the angular frequency calculation unit 60, thestorage unit 90, the voltage command calculation unit 91, and thevoltage command output unit 10 as the respective units forming thecontrol device for an AC rotating machine are shown, respectively.

A notation “execute” on the row (b) to the row (g), and the row (i)indicates execution of processing by each of the position detection unit3, the current detection unit 4, the first coordinate conversion unit 6,the current control unit 7, the second coordinate conversion unit 8, theangular frequency calculation unit 60, and the voltage commandcalculation unit 91. A blank field indicates that the processing is notexecuted. A notation “store” and a notation “hold” on the row (h) forthe storage unit 90 indicate the storage of the first three-phasevoltage command values vu1*, vv1*, and vw1* and the holding and theoutput of the stored first three-phase voltage command values vu1*,vv1*, and vw1* executed by the storage unit 90, respectively. A notation“first voltage command values” and a notation of “second voltage commandvalues” on the row (j) for the voltage command output unit 10 indicatethe selection and output of the first three-phase voltage command valuesvu1*, vv1*, and vw1* and the selection and output of the secondthree-phase voltage command values vu2*, vv2*, and vw2* executed by thevoltage command output unit 10, respectively.

As described above, the position detection unit 3, the current detectionunit 4, the first coordinate conversion unit 6, the current control unit7, and the second coordinate conversion unit 8 are the componentsrelating to only the generation of the first three-phase voltage commandvalues vu1*, vv1*, and vw1*. The angular frequency calculation unit 60,the storage unit 90, and the voltage command calculation unit 91 are thecomponents relating to only the generation of the second three-phasevoltage command values vu2*, vv2*, and vw2*. However, the storage unit90 is required to store the first three-phase voltage command valuesvu1*, vv1*, and vw1* in order to generate the second three-phase voltagecommand values vu2*, vv2*, and vw2*. Moreover, the angular frequencycalculation unit 60 is required to execute the processing each time thefirst operation cycle ΔT1 elapses in order to generate the secondthree-phase voltage command values vu2*, vv2*, and vw2*.

In consideration of this configuration, in the first embodiment, asshown in FIG. 6, when the first operation timing arrives, the positiondetection unit 3, the current detection unit 4, the first coordinateconversion unit 6, the current control unit 7, the second coordinateconversion unit 8, and the angular frequency calculation unit 60 areeach caused to execute the processing, and the storage unit 90 is causedto store the first three-phase voltage command values vu1*, vv1*, andvw1*. The voltage command output unit 10 is caused to select the firstthree-phase voltage command values vu1*, vv1*, and vw1*. The voltagecommand calculation unit 91 is caused not to execute the processing.Meanwhile, as shown in FIG. 6, when only the second operation timingarrives, the voltage command calculation unit 91 is caused to executethe processing of using the first three-phase voltage command valuesvu1*, vv1*, and vw1* held by the storage unit 90, and the voltagecommand output unit 10 is caused to select the second three-phasevoltage command values vu2*, vv2*, and vw2*. None of the positiondetection unit 3, the current detection unit 4, the first coordinateconversion unit 6, the current control unit 7, the second coordinateconversion unit 8, and the angular frequency calculation unit 60 iscaused to execute processing. In FIG. 6, a time point 8ΔT and later timepoints are omitted. The operations from the time point 0 to the timepoint 7ΔT are repeated after the time point 8ΔT.

In this manner, in the first embodiment, the processing content isdivided into the processing content executed by a first group includingthe position detection unit 3, the current detection unit 4, the firstcoordinate conversion unit 6, the current control unit 7, the secondcoordinate conversion unit 8, and the angular frequency calculation unit60, and the processing content executed by a second group including thevoltage command calculation unit 91. Those two groups are caused toselectively execute the processing at the arrival of at least one of thefirst operation timing and the second operation timing. As a result, inthe example shown in FIG. 6, the three-phase voltage command values vu*,vv*, and vw* on the stationary coordinates output from the voltagecommand output unit 10 are updated at the intervals of the secondoperation cycles ΔT2.

When the three-phase voltage command values vu*, vv*, and vw* on thestationary coordinates are updated at the intervals of the firstoperation cycles ΔT1, current pulsation occurs at the intervals of thefirst update cycles ΔT1, and noise thus occurs at (1/ΔT1) Hz. Meanwhile,when the three-phase voltage command values vu*, vv*, and vw* on thestationary coordinates are updated at the intervals of the secondoperation cycles ΔT2, current pulsation occurs at the second updatecycles ΔT2, and the frequency of the noise is thus (1/ΔT2) Hz. Arelationship of ΔT1>ΔT2 is satisfied, and a relationship of(1/ΔT1)<(1ΔT2) is thus satisfied. Thus, components of noise/vibrationcaused by the noise can be shifted to a higher frequency by adding theprocessing by the second group. As the frequency of sound increases, thesound is less likely to be heard by the human ears, and the sense ofdiscomfort given to the human by the noise is thus reduced.

The calculation for generating the second three-phase voltage commandvalues vu2*, vv2*, and vw2* is executed by the angular frequencycalculation unit 60 and the voltage command calculation unit 91. Thecalculation for obtaining the angular frequency ω executed by theangular frequency calculation unit 60 includes the one subtraction bythe subtractor 62 and the one multiplication by the proportional gainmultiplier 63. The calculation for obtaining the second three-phasevoltage command values vu2*, vv2*, and vw2* executed by the voltagecommand calculation unit 91 includes a total of four multiplications bythe proportional gain multiplier 70 and the multipliers 71, 72, and 73and a total of six additions and subtractions by the subtractors 74, 77,and 78 and the adders 75, 76, and 79. The total calculation amount ofthose calculations is much smaller than a total calculation amount inthe position detection unit 3, the current detection unit 4, the firstcoordinate conversion unit 6, the current control unit 7, and the secondcoordinate conversion unit 8. Thus, the sense of discomfort given to thehuman by the noise can be reduced while the calculation amount per unittime is suppressed.

As described above, the first coordinate conversion unit 6, the currentcontrol unit 7, the second coordinate conversion unit 8, the voltagecommand generation unit 9, the angular frequency calculation unit 60,and the voltage command output unit 10 are each implemented by thedigital circuit, which is, for example, a microcomputer. A requiredperformance level of the microcomputer is reduced by suppressing thecalculation amount per unit time. Therefore, a manufacturing cost of thecontrol device for an AC rotating machine can be further suppressed bysuppressing the calculation amount per unit time.

In the example illustrated in FIG. 6, the voltage command output unit 10selects the second three-phase voltage command values vu2*, vv2*, andvw2* as the three-phase voltage command values vu*, vv*, and vw* on thestationary coordinates at a center between the first operation timingsnext to each other. However, the timing for selecting the secondthree-phase voltage command values vu2*, vv2*, and vw2* between thefirst operation timings next to each other is not required to be thecenter. That is, for example, the second three-phase voltage commandvalues vu2*, vv2*, and vw2* may be selected when, for example, ΔT1/10,2ΔT⅕, or 3ΔT⅕ elapses after the arrival of the first operation timing.The number of selections of the second three-phase voltage commandvalues vu2*, vv2*, and vw2* may be two or more. As described above, thetiming for selecting the second three-phase voltage command values vu2*,vv2*, and vw2* between the first operation timings next to each otherand the number of those timings are not particularly limited.

FIG. 7 is a graph for showing an example of the first U-phase voltagecommand value vu1* on the stationary coordinates and the second U-phasevoltage command value vu2* on the stationary coordinates generated whenthe control device for an AC rotating machine according to the firstembodiment of the present invention is operated in accordance with thetime chart of FIG. 6. In the example of FIG. 7, a section in which thefirst U-phase voltage command value vu1* on the stationary coordinatesmonotonically increases is shown in an extracted form.

The first U-phase voltage command value vu1* on the stationarycoordinates is updated each time the first operation timing arrives. Asa result, as shown in FIG. 7, the first U-phase voltage command valuevu1* on the stationary coordinates is updated at the time points 0, 2ΔT,4ΔT, 6ΔT, . . . . Meanwhile, the second U-phase voltage command valuevu2* on the stationary coordinates is updated each time only the secondoperation timing arrives. As a result, as shown in FIG. 7, the secondU-phase voltage command value vu2* on the stationary coordinates isupdated at the time points ΔT, 3ΔT, 5ΔT, 7ΔT, . . . . The second U-phasevoltage command value vu2* is not updated at the time points 0, 2ΔT,4ΔT, 6ΔT, . . . , and is thus not changed until the next update. Thesecond U-phase voltage command value vu2* is obtained by correcting thephase of the U-phase memory voltage command value vu1 h*, and is thusdifferent from this U-phase memory voltage command value vu1 h*. Morespecifically, in FIG. 7, the second U-phase voltage command value vu2*has a larger value than that of the U-phase memory voltage command valuevu1h*.

The voltage command output unit 10 selects the first U-phase voltagecommand value vu1* at the time points 0, 2ΔT, 4ΔT, 6ΔT, . . . , andselects the second U-phase voltage command value vu2* at the time pointsΔT, 3ΔT, 5ΔT, 7ΔT, . . . . Consequently, the U-phase voltage commandvalue vu* on the stationary coordinates output from the voltage commandoutput unit 10 is the voltage command value updated each time the secondoperation timing arrives, that is, at the time points 0, ΔT, 2ΔT, 3ΔT,4ΔT, 5ΔT, 6ΔT, . . . . As a result, the U-phase voltage command valuevu* on the stationary coordinates is updated at the shorter cycles, thatis, at the higher frequency, and is input to the voltage applicationunit 1 as a smoother signal compared with a case of the update at thefirst operation timing.

In FIG. 7, only the first U-phase voltage command value vu1* and thesecond U-phase voltage command value vu2* are shown, but the other firstV-phase voltage command value vv1* and first W-phase voltage commandvalue vw1* have the same relationships with the second V-phase voltagecommand value vv2* and the second W-phase voltage command value vw2*.Therefore, the V-phase voltage command value vv* and the W-phase voltagecommand value vw* on the stationary coordinates are also updated at theshorter cycles, that is, at the higher frequency, and are input to thevoltage application unit 1 as smoother signals compared with the case ofthe update at the first operation timing.

In the first embodiment, as described above, the phases of the firstthree-phase voltage command values vu1*, vv1*, and vw1* are corrected,to thereby generate the second three-phase voltage command values vu2*,vv2*, and vw2*. This is for a reason described below.

Relationships between the d-axis current Id, the q-axis current Iq, ad-axis voltage Vd, and a q-axis voltage Vq are given by Expression (7)through use of a resistance Ra, a d-axis inductance Ld, a q-axisinductance Lq, and a magnetic flux

$\begin{matrix}\left\{ \begin{matrix}{{Vd} = {{RaId} - {\omega\;{LqIq}}}} \\{{Vq} = {{RaIq} + {\omega\;{LdId}} + {\omega\phi}}}\end{matrix} \right. & (7)\end{matrix}$

In a region in which the angular frequency ω is very low, the d-axisvoltage Vd is substantially proportional to the d-axis current Id, andthe q-axis voltage Vq is substantially proportional to the q-axiscurrent Iq. The phases of the three-phase currents and the phases of thethree-phase voltages substantially match each other on the stationarycoordinates. There exists a related art of adding a product of a changeamount of the detection current and a proportional gain to the firstvoltage command value on the stationary coordinates, to thereby generatethe second voltage command value based on this relationship (forexample, see Patent Literature 1). Description is now given in a form ofcomparison with this related art.

As the angular frequency ω becomes higher, influence of armaturereaction and an induced voltage becomes larger, and the differences inphase between the currents and the voltages become larger. For theconvenience of description, when it is assumed that the d-axis currentis zero, the voltage equation is given by Expression (8) below.

$\begin{matrix}\left\{ \begin{matrix}{{Vd} = {{- \omega}\;{LqIq}}} \\{{Vq} = {{RaIq} + {\omega\phi}}}\end{matrix} \right. & (8)\end{matrix}$

While the phase of the current is in the q-axis direction, the phase ofthe voltage is in a direction advanced with respect to the q-axisdirection. As an example, waveforms of the three-phase currents and thethree-phase voltages different in phase by 10 degrees in the steadystate are shown in FIG. 8. In FIG. 8, the top graph indicates thethree-phase currents on the stationary coordinates, and the bottom graphindicates the three-phase voltages on the stationary coordinates. InFIG. 8, it is shown that, for example, when the voltage command valueson the bottom graph are given, the currents on the top graph areobtained under this steady state in which this angular frequency doesnot change.

When the detection currents are fed back so as to generate the voltagecommand values, differences actually occur in accordance with a timeconstant of the control response. That is, expected voltage commandvalues and voltage command values actually generated do not match eachother, and the differences thus occur therebetween. However, for theconvenience of the description, the occurrence of the differences isneglected in this description.

In FIG. 8, it is assumed that the first voltage command values on thestationary coordinates are generated at a timing “a”, and the secondvoltage command values on the stationary coordinates are generated at atiming “b”. In this case, when expected voltage command values are givenat the timing “a”, the U-phase current increases, the V-phase currentincreases, and the W-phase current decreases during the transition tothe timing “b”. The second voltage command value on the stationarycoordinates at the timing “b” can be obtained by adding the result ofmultiplication of the change amount of the detection current on thestationary coordinates by the proportional gain to the first voltagecommand value on the stationary coordinates at the timing “a”.

The change amounts of the detection current on the stationarycoordinates are positive in the U phase, positive in the V phase, andnegative in the W phase in the transition from the timing “a” to thetiming “b”. Therefore, the voltage command values on the stationarycoordinates at the timing “b” are increased in the U phase, increased inthe V phase, and decreased in the W phase with respect to the voltagecommand values at the timing “a”. However, as shown on the bottom graphof FIG. 8, voltage command values required to be obtained on thestationary coordinates at the timing “b” are decreased in the U phase,increased in the V phase, and decreased in the W phase with respect tothe voltage command values at the timing “a”. Therefore, in the relatedart, unnecessary current fluctuation is caused in a high rotation regionhaving the large difference in phase between the currents and thevoltages. In order to suppress the unnecessary current fluctuation evenin the high rotation region, a mechanism for suppressing the fluctuationis required, and a calculation amount actually required thus increases.The unnecessary current fluctuation causes the occurrence of the noisein the AC rotating machine 2.

Meanwhile, in the first embodiment, the second three-phase voltagecommand values are generated without using the detection currents.Therefore, the phase differences changing in accordance with the angularfrequency between the currents and the voltages are not required to beconsidered. Moreover, the first three-phase voltage command values arevalues basically changing cyclically. In consideration of this fact, asdescribed above, the second three-phase voltage command values canappropriately be generated with the relatively small calculation amountat the timing different from the timing at which the first three-phasevoltage command values are generated. Therefore, the appropriate secondthree-phase voltage command values can be generated while thecalculation amount per unit time is suppressed compared with theabove-mentioned related art.

The first embodiment may be combined with the above-mentioned relatedart or other related art in accordance with a situation. For example, inFIG. 6, when the detection currents are used to generate the secondthree-phase voltage command values at the timings of the time points2ΔT, 6ΔT, . . . , feedback based on the detection currents is to beexecuted at each 2ΔT. As a result, the sense of discomfort caused by thenoise can be reduced while the increase in calculation amount issuppressed in addition to the suppression of a decrease inresponsiveness.

Second Embodiment

In a second embodiment of the present invention, the mechanism forgenerating the second three-phase voltage command values vu2*, vv2*, andvw2* is different from that in the above-mentioned first embodiment.Description is now given while focusing on only this mechanism. The samereference symbols are used for the same or substantially the samecomponents as those in the above-mentioned first embodiment.

FIG. 9 is a block diagram for illustrating a configuration example of avoltage command calculation unit 91 a in the second embodiment. First,referring to FIG. 9, a specific description is given of the voltagecommand calculation unit 91 a in the second embodiment.

As illustrated in FIG. 9, the voltage command calculation unit 91 a inthe second embodiment includes a first-time-point voltage commandcalculation unit 911, a second-time-point voltage command calculationunit 912, a third-time-point voltage command calculation unit 913, and asecond voltage command selection unit 914. The voltage commandcalculation unit 91 a is also implemented on, for example, amicrocomputer, as in the voltage command calculation unit 91 in theabove-mentioned first embodiment.

The three-phase memory voltage command values vu1h*, vv1h*, and vw1h*from the storage unit 90 and the angular frequency ω from the angularfrequency calculation unit 60 are input to each of the first-time-pointvoltage command calculation unit 911, the second-time-point voltagecommand calculation unit 912, and the third-time-point voltage commandcalculation unit 913. The first-time-point voltage command calculationunit 911, the second-time-point voltage command calculation unit 912,and the third-time-point voltage command calculation unit 913 areconfigured to correct the phases of the three-phase memory voltagecommand values vu1h*, vv1h*, and vw1h* based on the angular frequency ω,to thereby generate first-time-point voltage command values vu21*,vv21*, and vw21*, second-time-point voltage command values vu22*, vv22*,and vw22*, and third-time-point voltage command values vu23*, vv23*, andvw23*, respectively, as in the above-mentioned first embodiment. All ofthose generated second voltage command values correspond to thirdvoltage command values on the stationary coordinates, and are output tothe second voltage command selection unit 914.

Description is now given of the first time point, the second time point,and the third time point. The voltage command calculation unit 91 aoperates when the second operation timing arrives as in theabove-mentioned first embodiment. In the second embodiment, the secondoperation cycle ΔT2 is set to a cycle of ¼ time the first operationcycle ΔT1. As a result, three second operation timings exist between thetwo first operation timings next to each other.

The three second operation timings existing between the two firstoperation timings next to each other equally divide the period betweenthose two first operation timings next to each other, namely, the firstoperation cycle ΔT1, into four periods, by setting the second operationcycle ΔT2 to the cycle of ¼ time the first operation cycle ΔT1. As aresult, the first time point is a time point after the second operationcycle ΔT2 elapses from the first operation timing existing before.Similarly, the second time point is a time point after 2ΔT2, which istwice the second operation cycle ΔT2, elapses from the first operationtiming existing before. The third time point is a time point after 3ΔT2,which is three times the second operation cycle ΔT2, elapses from thefirst operation timing existing before. All of the first time point, thesecond time point, and the third time point are the second operationtimings.

Only the first-time-point voltage command calculation unit 911 operatesat the first time point, and the first-time-point voltage command valuesvu21*, vv21*, and vw21* are generated, and are then output. Thefirst-time-point voltage command values vu21*, vv21, and vw21* aredigital signals, and include a first-time-point U-phase voltage commandvalue vu21*, a first-time-point V-phase voltage command value vv21*, anda first-time-point W-phase voltage command value vw21*.

Only the second-time-point voltage command calculation unit 912 operatesat the second time point, and the second-time-point voltage commandvalues vu22*, vv22*, and vw22* are generated, and are then output. Thesecond-time-point voltage command values vu22*, vv22*, and vw22* arealso digital signals, and include a second-time-point U-phase voltagecommand value vu22*, a second-time-point V-phase voltage command valuevv22*, and a second-time-point W-phase voltage command value vw22*.

Only the third-time-point voltage command calculation unit 913 operatesat the third time point, and the third-time-point voltage command valuesvu23*, vv23*, and vw23* are generated, and are then output. Thethird-time-point voltage command values vu23*, vv23*, and vw23* are alsodigital signals, and include a third-time-point U-phase voltage commandvalue vu23*, a third-time-point V-phase voltage command value vv23*, anda third-time-point W-phase voltage command value vw23*.

The angular frequency calculation unit 60 configured to output theangular frequency ω operates when the first operation timing arrives asin the above-mentioned first embodiment. As a result, the angularfrequency ω has the same value at the first time point, the second timepoint, and the third time point.

The first-time-point voltage command calculation unit 911, thesecond-time-point voltage command calculation unit 912, and thethird-time-point voltage command calculation unit 913 are configured toexecute the calculation as given by Expression (6). Therefore, theconfiguration of each of the first-time-point voltage commandcalculation unit 911, the second-time-point voltage command calculationunit 912, and the third-time-point voltage command calculation unit 913is basically the same as that of the voltage command calculation unit 91in the above-mentioned first embodiment. Therefore, a detaileddescription thereof is omitted. However, the first to third time pointsare the second operation timings different from one another, and thusproportional gains to be used for the calculation are different from oneanother. That is, the very short period ΔT in Expression (6) is thesecond operation cycle ΔT2 at the first time point, is twice the secondoperation cycle ΔT2 at the second time point, and is three times thesecond operation cycle ΔT2 at the third time point.

The approximation given by Expression (4) is also used in the secondembodiment as in the above-mentioned first embodiment, but Expression(5), which is the calculation expression for the phase correction, maybe used in place of Expression (4) for the approximation. Further, theapproximation given by Expression (2) may be replaced by, for example,the approximation of “cos(ωΔT)≈1−(ωΔT)²÷2” based on the Maclaurin'sexpansion, to thereby derive an expression for the phase correction.

The second voltage command selection unit 914 is configured to selectthe first-time-point voltage command values vu21*, vv21*, and vw21* atthe first time point, to output the selected first-time-point voltagecommand values vu21*, vv21*, and vw21* as the second three-phase voltagecommand values vu2*, vv2*, and vw2*. Similarly, the second voltagecommand selection unit 914 is configured to select the second-time-pointvoltage command values vu22*, vv22*, and vw22* at the second time point,to output the selected second-time-point voltage command values vu22*,vv22*, and vw22* as the second three-phase voltage command values vu2*,vv2*, and vw2*. Similarly, the second voltage command selection unit 914is configured to select the third-time-point voltage command valuesvu23*, vv23*, and vw23* at the third time point, to output the selectedthird-time-point voltage command values vu23*, vv23*, and vw23* as thesecond three-phase voltage command values vu2*, vv2*, and vw2*.

FIG. 10 is an example of a time chart for showing operation examples ofthe respective units in the control device for an AC rotating machineaccording to the second embodiment of the present invention. Asdescribed above, this time chart is a time chart in a case in which thesecond operation cycle ΔT2 is set to ¼ time the first operation cycleΔT1. In this case, it is assumed that the first operation cycle ΔT1 andthe second operation cycle ΔT2 are generated from the referenceoperation cycle ΔT serving as a reference timing of the operation, andthe second operation cycle ΔT2 is set to the reference operation cycleΔT. On the basis of this assumption, the second operation timing arrivesfour times while the first operation timing arrives each time the firstoperation cycle ΔT1 elapses. One of the four times of the secondoperation timings arrives at the same timing as the first operationtiming.

In FIG. 10, time points (seconds) having the reference operation cycleΔT as a unit are shown as 0, ΔT, 2ΔT, . . . , 9ΔT on a row (a). On a row(b) to a row (m), operation states at each time point of the positiondetection unit 3, the current detection unit 4, the first coordinateconversion unit 6, the current control unit 7, the second coordinateconversion unit 8, the angular frequency calculation unit 60, thestorage unit 90, the first-time-point voltage command calculation unit911, the second-time-point voltage command calculation unit 912, thethird-time-point voltage command calculation unit 913, the secondvoltage command selection unit 914, and the voltage command output unit10 as the respective units forming the control device for an AC rotatingmachine are shown, respectively.

A notation “execute” on the row (b) to the row (g), and the row (i) tothe row (k) indicates execution of processing by each of the positiondetection unit 3, the current detection unit 4, the first coordinateconversion unit 6, the current control unit 7, the second coordinateconversion unit 8, the angular frequency calculation unit 60, thefirst-time-point voltage command calculation unit 911, thesecond-time-point voltage command calculation unit 912, and thethird-time-point voltage command calculation unit 913. A blank fieldindicates that the processing is not executed. A notation “store” and anotation “hold” on the row (h) for the storage unit 90 indicate thestorage of the first three-phase voltage command values vu1*, vv1*, andvw1* and the holding and the output of the stored first three-phasevoltage command values vu1*, vv1*, and vw1* executed by the storage unit90, respectively. Notations “first-time-point voltage command values,”“second-time-point voltage command values,” and “third-time-pointvoltage command values” on the row (l) for the second voltage commandselection unit 914 indicate the selection of the first-time-pointvoltage command values vu21*, vv21*, and vw21*, the second-time-pointvoltage command values vu22*, vv22*, and vw22*, and the third-time-pointvoltage command values vu23*, vv23*, and vw23* executed by the secondvoltage command selection unit 914, respectively. A notation “firstvoltage command values” and a notation of “second voltage commandvalues” on the row (m) for the voltage command output unit 10 indicatethe selection and output of the first three-phase voltage command valuesvu1*, vv1*, and vw1* and the selection and output of the secondthree-phase voltage command values vu2*, vv2*, and vw2* executed by thevoltage command output unit 10, respectively.

Also in the second embodiment, as shown in FIG. 10, the positiondetection unit 3, the current detection unit 4, the first coordinateconversion unit 6, the current control unit 7, the second coordinateconversion unit 8, and the angular frequency calculation unit 60 areeach caused to execute the processing, and the storage unit 90 is causedto store the first three-phase voltage command values vu1*, vv1*, andvw1* when the first operation timing arrives. The voltage command outputunit 10 is caused to select the first three-phase voltage command valuesvu1*, vv1*, and vw1*. The first-time-point voltage command calculationunit 911, the second-time-point voltage command calculation unit 912,and the third-time-point voltage command calculation unit 913 are causednot to execute the processing.

Meanwhile, when only the second operation timing arrives, as shown inFIG. 10, the first-time-point voltage command calculation unit 911, thesecond-time-point voltage command calculation unit 912, and thethird-time-point voltage command calculation unit 913 are caused tosequentially execute the processing of using the first three-phasevoltage command values vu1*, vv1*, and vw1* held by the storage unit 90.None of the position detection unit 3, the current detection unit 4, thefirst coordinate conversion unit 6, the current control unit 7, thesecond coordinate conversion unit 8, and the angular frequencycalculation unit 60 is caused to execute processing. As a result, in thesecond embodiment, the calculation amount required in order to generatethe second three-phase voltage command values vu2*, vv2*, and vw2*selected by the voltage command output unit 10 is further suppressed. InFIG. 10, a time point 10ΔT and later time points are omitted. Theoperations from the time point 2ΔT to the time point 9ΔT are repeatedafter the time point 10ΔT.

When the three-phase voltage command values vu*, vv*, and vw* on thestationary coordinates are updated at the same time intervals as thosein the above-mentioned first embodiment, the first operation cycle ΔT1in the second embodiment can be twice as long as that in theabove-mentioned first embodiment. Therefore, in the second embodiment,the calculation amount per unit time can be further suppressed comparedwith the above-mentioned first embodiment.

FIG. 11 is a graph for showing an example of the first U-phase voltagecommand value vu1* on the stationary coordinates and the second U-phasevoltage command value vu2* on the stationary coordinates generated whenthe control device for an AC rotating machine according to the secondembodiment of the present invention is operated in accordance with thetime chart of FIG. 10. Also in the example of FIG. 11, a section inwhich the first U-phase voltage command value vu1′ on the stationarycoordinates monotonically increases is shown in an extracted form as inthe above-mentioned example of FIG. 7.

The first U-phase voltage command value vu1* on the stationarycoordinates is updated each time the first operation timing arrives. Asa result, as shown in FIG. 11, the first U-phase voltage command valuevu1* on the stationary coordinates is updated at the time points 0, 4ΔT,8ΔT, . . . . Meanwhile, the second U-phase voltage command value vu2* onthe stationary coordinates is updated each time only the secondoperation timing arrives. As a result, as shown in FIG. 11, the secondU-phase voltage command value vu2* on the stationary coordinates isupdated at the time points ΔT, 2ΔT, 3ΔT, 5ΔT, 6ΔT, 7ΔT, 9ΔT, . . . .More specifically, the second U-phase voltage command value vu2* isupdated through the generation of the first-time-point voltage commandvalue vu21* at the time points ΔT, 5ΔT, and 9ΔT, through the generationof the second-time-point voltage command value vu22* at the time points2ΔT and 6ΔT, and through the generation of the third-time-point voltagecommand value vu23* at the time points 3ΔT and 7ΔT. The second U-phasevoltage command value vu2* is not updated at the time points 0, 4ΔT,8ΔT, . . . . Therefore, the second U-phase voltage command value vu2*does not change, and the third-time-point voltage command value vu23* isthus held until the next update.

The first-time-point voltage command values vu21*, vv21*, and vw21*, thesecond-time-point voltage command values vu22*, vv22*, and vw22*, andthe third-time-point voltage command values vu23*, vv23*, and vw23* aregenerated through use of the proportional gains different from oneanother, and the value of the second U-phase voltage command value vu2*thus changes in accordance with the time point. In FIG. 11, the secondU-phase voltage command value vu2* has such a magnitude relationship of“first-time-point voltage command value vu21*<second-time-point voltagecommand value vu22*<third-time-point voltage command value vu23*.”

The voltage command output unit 10 selects the first U-phase voltagecommand value vu1* at the time points 0, 4ΔT, 8ΔT, . . . , and selectsthe second U-phase voltage command value vu2* at the time points ΔT,2ΔT, 3ΔT, 5ΔT, 6ΔT, 7ΔT, 9ΔT, . . . . Consequently, the U-phase voltagecommand value vu* on the stationary coordinates output from the voltagecommand output unit 10 is the voltage command value updated each timethe second operation timing arrives, that is, at the time points 0, ΔT,2ΔT, 3ΔT, 4ΔT, 5ΔT, 6ΔT, 7ΔT, 8ΔT, 9ΔT . . . . As a result, the U-phasevoltage command value vu* on the stationary coordinates is updated atthe shorter cycles, that is, at the higher frequency, and is input tothe voltage application unit 1 as a smoother signal compared with a caseof the update only at the first operation timing.

In FIG. 11, only the first U-phase voltage command value vu1* and thesecond U-phase voltage command value vu2* are shown, but the other firstV-phase voltage command value vv1* and first W-phase voltage commandvalue vw1* have the same relationships with the second V-phase voltagecommand value vv2* and the second W-phase voltage command value vw2*.Therefore, the V-phase voltage command value vv* and the W-phase voltagecommand value vw* on the stationary coordinates are also updated at theshorter cycles, that is, at the higher frequency, and are input to thevoltage application unit 1 as smoother signals compared with the case ofthe update only at the first operation timing.

In the second embodiment, as shown in FIG. 10, the first-time-pointvoltage command calculation unit 911, the second-time-point voltagecommand calculation unit 912, and the third-time-point voltage commandcalculation unit 913 are selectively operated. Therefore, it is notrequired to arrange the second voltage command selection unit 914 on asubsequent stage. That is, the second voltage command selection unit 914may be configured to control the operation of each of thefirst-time-point voltage command calculation unit 911, thesecond-time-point voltage command calculation unit 912, and thethird-time-point voltage command calculation unit 913. Moreover, whenthe second voltage command selection unit 914 is arranged on thesubsequent stage, the second voltage command selection unit 914 may beconfigured to simultaneously operate the first-time-point voltagecommand calculation unit 911, the second-time-point voltage commandcalculation unit 912, and the third-time-point voltage commandcalculation unit 913. This is because the second voltage commandselection unit 914 is only required to change the object to be selectedeach time the second operation timing arrives.

Third Embodiment

In a third embodiment of the present invention, the mechanism forgenerating the second three-phase voltage command values vu2*, vv2*, andvw2* is different from that in the above-mentioned first and secondembodiments. Description is now given while focusing on only thismechanism. The same reference symbols are used for the same orsubstantially the same components as those in the above-mentioned firstembodiment.

FIG. 12 is a block diagram for illustrating an overall configurationexample of a control device for an AC rotating machine according to thethird embodiment of the present invention. In the third embodiment, asillustrated in FIG. 12, the voltage command generation unit 9 and thevoltage command output unit 10 are different from those in theabove-mentioned first embodiment. Therefore, the voltage commandgeneration unit 9 and the voltage command output unit 10 are focused inthis embodiment.

In the above-mentioned first and second embodiments, the generation ofthe second three-phase voltage command values vu2*, vv2*, and the vw2′through use of the angular frequency ω output by the angular frequencycalculation unit 60 is executed based on the correction of the phases ofthe first three-phase voltage command values vu1*, vv1*, and vw1*.Meanwhile, in the third embodiment, the three-phase voltage commandvalues vu*, vv*, and vw* output by the voltage command output unit 10are used as the objects of the correction of the phases. Therefore, eachtime the three-phase voltage command values vu*, vv*, and vw* output bythe voltage command output unit 10 are updated, the voltage commandgeneration unit 9 is configured to hold the three-phase voltage commandvalues vu*, vv*, and vw* after the update. The voltage commandgeneration unit 9 unconditionally holds the three-phase voltage commandvalues vu*, vv*, and vw* after the update, and the voltage commandoutput unit 10 does not thus include the switch flag output unit 10 sf.

Meanwhile, the voltage command generation unit 9 includes voltagecommand value delay-and-hold calculation units 92, 93, and 94 configuredto hold the three-phase voltage command values vu*, vv*, and vw* outputby the voltage command output unit 10 in place of the storage unit 90.The voltage command value delay-and-hold calculation units 92, 93, and94 are used to hold the three-phase voltage command values vu*, vv*, andvw* in the respective phases. Specifically, the voltage command valuedelay-and-hold calculation unit 92 is used to hold the voltage commandvalue vu*. The voltage command value delay-and-hold calculation unit 93is used to hold the voltage command value vv*. The voltage command valuedelay-and-hold calculation unit 94 is used to hold the voltage commandvalue vw*.

The voltage command value delay-and-hold calculation units 92, 93, and94 are memories configured to delay the input data by a delay timeinterval corresponding to the second operation cycle ΔT2 and then holdthe delayed input data, or to hold the input data and then delay theheld input data by the delay time interval, to thereby reflect thedelayed input data to the output. As a result, the three-phase voltagecommand values vu1h*, vv1h*, and vw1h* output by the voltage commandvalue delay-and-hold calculation units 92, 93, and 94 are changed at thearrival of the second operation timing. Therefore, the three-phasevoltage command values vu1h*, vv1h*, and vw1h* output from the voltagecommand value delay-and-hold calculation units 92, 93, and 94 to thevoltage command calculation unit 91 when the second operation timingarrives are the three-phase voltage command values vu*, vv*, and vw*output from the voltage command output unit 10 when the second operationtiming immediately before the second operation timing arrives.

The voltage command calculation unit 91 is configured to use thethree-phase voltage command values vu1h*, vv1h*, and vw1h* output fromthe voltage command value delay-and-hold calculation units 92, 93, and94 and the angular frequency ω output by the angular frequencycalculation unit 60 so as to generate the three-phase voltage commandvalues vu2*, vv2*, and vw2* when only the second operation timingarrives as in the above-mentioned first embodiment. Therefore, theconfiguration is the same as that in the above-mentioned firstembodiment.

FIG. 13 is an example of a time chart for showing operation examples ofthe respective units in the control device for an AC rotating machineaccording to the third embodiment of the present invention. This timechart is a time chart in a case in which the second operation cycle ΔT2is set to ⅕ time the first operation cycle ΔT1. Also in this case, it isassumed that the first operation cycle ΔT1 and the second operationcycle ΔT2 are generated from the reference operation cycle ΔT serving asa reference timing of the operation, and the second operation cycle ΔT2is set to the reference operation cycle ΔT. On the basis of thisassumption, the second operation timing arrives fifth times while thefirst operation timing arrives each time the first operation cycle ΔT1elapses. One of the fifth times of the second operation timings arrivesat the same timing as the first operation timing.

In FIG. 13, time points (seconds) having the reference operation cycleΔT as a unit are shown as 0, ΔT, 2ΔT, . . . , 11ΔT on a row (a). On arow (b) to a row (j), operation states at each time point of theposition detection unit 3, the current detection unit 4, the firstcoordinate conversion unit 6, the current control unit 7, the secondcoordinate conversion unit 8, the angular frequency calculation unit 60,the voltage command value delay-and-hold calculation units 92 to 94, thevoltage command calculation unit 91, and the voltage command output unit10 as the respective units forming the control device for an AC rotatingmachine are shown, respectively.

Notation “delay and hold” on the row (h) for the voltage command valuedelay-and-hold calculation units 92 to 94 indicates that the three-phasevoltage command values vu*, vv*, and vw* are held, and the three-phasevoltage command values vu*, vv*, and vw* delayed by the delay timeinterval corresponding to the second operation cycle ΔT2 and held areoutput as the three-phase voltage command values vu1h*, vv1h*, andvw1h*. The voltage command output unit 10 indicated on the row (j)selects and outputs the first three-phase voltage command values vu1*,vv1*, and vw1* when the first operation timing arrives, and selects andoutputs the second three-phase voltage command values vu2*, vv2*, andvw2* when only the second operation timing arrives.

Also in the third embodiment, as shown in FIG. 13, the positiondetection unit 3, the current detection unit 4, the first coordinateconversion unit 6, the current control unit 7, the second coordinateconversion unit 8, and the angular frequency calculation unit 60 areeach caused to execute the processing when the first operation timingarrives. The voltage command output unit 10 is caused to select thefirst three-phase voltage command values vu1*, vv1*, and vw1*. Thevoltage command calculation unit 91 is caused not to execute theprocessing.

Meanwhile, as shown in FIG. 13, when only the second operation timingarrives, the processing of using the first three-phase voltage commandvalues vu1h*, vv1h*, and vw1h* output by the voltage command valuedelay-and-hold calculation units 92 to 94 are executed. None of theposition detection unit 3, the current detection unit 4, the firstcoordinate conversion unit 6, the current control unit 7, the secondcoordinate conversion unit 8, and the angular frequency calculation unit60 is caused to execute processing. As a result, also in the thirdembodiment, the calculation amount required in order to generate thesecond three-phase voltage command values vu2*, vv2*, and vw2* selectedby the voltage command output unit 10 is further suppressed as in theabove-mentioned second embodiment. In FIG. 13, a time point 12ΔT andlater time points are omitted. For example, the operations from the timepoint 7ΔT to the time point 11ΔT are repeated after the time point 12ΔT.

When the three-phase voltage command values vu*, vv*, and vw* on thestationary coordinates are updated at the same time intervals as thosein the above-mentioned first embodiment, the first operation cycle ΔT1in the third embodiment can be two and a half times as long as that inthe above-mentioned first embodiment. Therefore, in the thirdembodiment, the calculation amount per unit time can be furthersuppressed compared with the above-mentioned first embodiment.

FIG. 14 is a graph for showing an example of the first U-phase voltagecommand value vu1* on the stationary coordinates and the second U-phasevoltage command value vu2* on the stationary coordinates generated whenthe control device for an AC rotating machine according to the thirdembodiment of the present invention is operated in accordance with thetime chart of FIG. 13. Also in the example of FIG. 14, a section inwhich the first U-phase voltage command value vu1* on the stationarycoordinates monotonically increases is shown in an extracted form as inthe above-mentioned examples of FIG. 7 and FIG. 11.

The first U-phase voltage command value vu1* on the stationarycoordinates is updated each time the first operation timing arrives. Asa result, as shown in FIG. 14, the first U-phase voltage command valuevu1* on the stationary coordinates is updated at the time points 0, 5ΔT,10ΔT, . . . Meanwhile, the second U-phase voltage command value vu2* onthe stationary coordinates is updated each time only the secondoperation timing arrives. As a result, as shown in FIG. 14, the secondU-phase voltage command value vu2* on the stationary coordinates isupdated at the time points ΔT, 2ΔT, 3ΔT, 4ΔT, 6ΔT, 7ΔT, 8ΔT, 9ΔT, 11ΔT,. . . . The second U-phase voltage command value vu2* is not updated atthe time points 0, 5ΔT, 10ΔT, . . . , and does not thus change until thenext update. The second U-phase voltage command value vu2* is generatedthrough use of the voltage command value vu* output immediately before.Therefore, the value of the second U-phase voltage command value vu2*changes in accordance with the time point.

The voltage command output unit 10 selects the first U-phase voltagecommand value vu1* at the time points 0, 5ΔT, 10ΔT, . . . , and selectsthe second U-phase voltage command value vu2* at the time points ΔT,2ΔT, 3ΔT, 4ΔT, 6ΔT, 7ΔT, 8ΔT, 9ΔT, 11ΔT, . . . Consequently, the U-phasevoltage command value vu* on the stationary coordinates output from thevoltage command output unit 10 is the voltage command value updated eachtime the second operation timing arrives, that is, at the time points 0,ΔT, 2ΔT, 3ΔT, 4ΔT, 5ΔT, 6ΔT, 7ΔT, 8ΔT, 9ΔT, 10ΔT, 11ΔT, . . . . As aresult, the U-phase voltage command value vu* on the stationarycoordinates is updated at the shorter cycles, that is, at the higherfrequency, and is input to the voltage application unit 1 as a smoothersignal compared with a case of the update only at the first operationtiming.

In FIG. 14, only the first U-phase voltage command value vu1* and thesecond U-phase voltage command value vu2* are shown, but the other firstV-phase voltage command value vv1* and first W-phase voltage commandvalue vw1* have the same relationships with the second V-phase voltagecommand value vv2* and the second W-phase voltage command value vw2*.Therefore, the V-phase voltage command value vv* and the W-phase voltagecommand value vw* on the stationary coordinates are also updated at theshorter cycles, that is, at the higher frequency, and are input to thevoltage application unit 1 as smoother signals compared with the case ofthe update at the first operation timing.

In the above-mentioned first to third embodiments, the first coordinateconversion unit 6, the current control unit 7, the second coordinateconversion unit 8, the voltage command generation unit 9, the voltagecommand output unit 10, and the angular frequency calculation unit 60are each implemented by the digital circuit, which is, for example, amicrocomputer. When each of those units 6 to 10 and 60 is implemented bya subprogram, each of the units 6 to 10 and 60 can be caused toappropriately operate by sharing data required among the subprograms.

In this case, the subprograms can be divided into a first group, whichis the object to be operated at the first operation timing, and thesecond group, which is the object to be operated at the second operationtiming. When the subprograms are divided into the two groups as describeabove, the execution intervals of the subprograms are only required tobe the second operation cycles ΔT2. As described above, the positiondetection unit 3 is configured to output the rotation position θ eachtime the first operation cycle ΔT1 elapses. Therefore, the group to beexecuted may be selected in accordance with the absence or presence ofthe output of the rotation position θ at the execution timing of thesubprograms. The selection of the group to be executed corresponds tothe function of the voltage command output unit 10. Therefore, thevoltage command output unit 10 may be arranged at a location differentfrom the subsequent stage of the second coordinate conversion unit 8 andthe voltage command generation unit 9.

Fourth Embodiment

The above-mentioned first to third embodiments relate to the controldevices for an AC rotating machine. Those control devices for an ACrotating machine are applicable to a device configured to use the ACrotating machine as power. A fourth embodiment of the present inventionis an example in which the control device for an AC rotating machine isapplied as a control device for an electric power steering system in avehicle, for example, an automobile, which is configured to use the ACrotating machine as a power source of the electric power steeringsystem. Therefore, the fourth embodiment corresponds to the controldevice for an electric power steering system according to the firstembodiment of the present invention. Also in this embodiment, the samereference symbols are assigned to the same or substantially the samecomponents as those in the above-mentioned first embodiment, anddescription is given while focusing on only differences from theabove-mentioned first embodiment.

FIG. 15 is a block diagram for illustrating an overall configurationexample of the control device for an electric power steering systemaccording to the fourth embodiment of the present invention. The controldevice for an electric power steering system according to this fourthembodiment corresponds to the above-mentioned first embodiment appliedas the control device for an electric power steering system. Therefore,the fourth embodiment includes all of the components illustrated inFIG. 1. In FIG. 15, components having the same reference symbols asthose in the above-mentioned first embodiment are the same orcorresponding components. As illustrated in FIG. 15, in the fourthembodiment, a steering wheel 150, a torque detection unit 151, a currentcommand calculation unit 152, and gears 153 are added compared with theabove-mentioned first embodiment.

When a driver operates the steering wheel 150 to generate a steeringtorque in a steering mechanism of the vehicle, this steering torque isdetected by the torque detection unit 151. When the torque detectionunit 151 detects this steering torque, the torque detection unit 151outputs a detection result as a detection torque. This detection torqueis output in a form of a digital signal from the torque detection unit151 to the current command calculation unit 152.

The AC rotating machine 2 is the power source configured to generate anassist torque for assisting the steering torque. The assist torquegenerated by this AC rotating machine 2 is transmitted to a steeringmechanism for tires 154 of the vehicle through the gears 153. Therefore,in order to cause the AC rotating machine 2 to generate the assisttorque for assisting the steering torque, the current commandcalculation unit 152 uses the detection torque output from the torquedetection unit 151 so as to calculate the two-phase current commandvalues id* and iq* on the rotational coordinates, and outputs thecalculated two-phase current command values id* and iq* to the currentcontrol unit 7.

In the above-mentioned first embodiment, the first coordinate conversionunit 6, the current control unit 7, the second coordinate conversionunit 8, the voltage command generation unit 9, the voltage commandoutput unit 10, and the angular frequency calculation unit 60 are eachimplemented by the digital circuit, which is, for example, amicrocomputer. The current command calculation unit 152 is alsoimplemented by the digital circuit.

The current command calculation unit 152 is configured to use thedetection torque input from the torque detection unit 151 so as togenerate the two-phase current command values id* and iq* on therotational coordinates, to output the generated two-phase currentcommand values id* and iq* on the rotational coordinates to the currentcontrol unit 7. As a result, the current control unit 7 uses thetwo-phase current command values id* and iq* on the rotationalcoordinates input from the current command calculation unit 152 and thetwo-phase detection currents id and iq input from the first coordinateconversion unit 6 so as to generate the two-phase voltage command valuesvd1* and vq1* on the rotational coordinates, and outputs the generatedtwo-phase voltage command values vd1* and vq1* to the second coordinateconversion unit 8. The two-phase voltage command values vd1* and vq1* onthe rotational coordinates generated by the current control unit 7 aredigital signals.

The second coordinate conversion unit 8 is configured to input thetwo-phase voltage command values vd1* and vq1* on the rotationalcoordinates output by the current control unit 7, to thereby generateand output the first three-phase voltage command values vu1*, vv1*, andvw1* on the stationary coordinates. Consequently, the voltage commandgeneration unit 9 uses the first three-phase voltage command valuesvu1*, vv1*, and vw1* output by the second coordinate conversion unit 8and the angular frequency ω output by the angular frequency calculationunit 60 so as to generate the second three-phase voltage command valuesvu2*, vv2*, and vw2* on the stationary coordinates. As a result, thevoltage application unit 1 uses the first three-phase voltage commandvalues vu1*, vv1*, and vw1* or the second three-phase voltage commandvalues vu2*, vv2*, and vw2* output by the voltage command output unit 10as the three-phase voltage command values vu*, vv*, and vw* on thestationary coordinates so as to generate the three-phase AC voltages vu,vv, and vw, and applies the three-phase AC voltages vu, vv, and vw tothe AC rotating machine 2.

The cycle at which the first three-phase voltage command values vu1*,vv1*, and vw1* is updated by the second coordinate conversion unit 8 byusing the two-phase voltage command values vd1* and vq1* output by thecurrent control unit is the first operation cycle ΔT1. Therefore, whenthe calculation cycle of the current command calculation unit 152 isshorter than the first operation cycle ΔT1, the current commandcalculation unit 152 may execute useless calculation. This is becausethe two-phase voltage command values vd1* and vq1* calculated by thecurrent command calculation unit 152 are not always used. Thus, it ispreferred that the calculation cycle of the current command calculationunit 152 be equal to or longer than the first operation cycle ΔT1 inorder to avoid the unnecessary calculation load.

The noise emitted by the AC rotating machine 2 can greatly be reducedthrough the application of the above-mentioned first embodiment to thecontrol device for an electric power steering system. Therefore, thesense of discomfort given to the driver by the noise emitted by the ACrotating machine 2 can be avoided, or can greatly be reduced. Moreover,the calculation amount per unit time can also greatly be reduced. Whenthe calculation cycle of the current command calculation unit 152 isequal to or longer than the first operation cycle ΔT1, it is possible tofurther suppress the calculation amount per unit time while reducing thesense of discomfort given to the driver by the noise emitted by the ACrotating machine 2.

In the fourth embodiment, the above-mentioned first embodiment isapplied so as to form the control device for an electric power steeringsystem, but the above-mentioned second embodiment or the above-mentionedthird embodiment may be applied so as to form the control device for anelectric power steering system.

REFERENCE SIGNS LIST

1 voltage application unit, 2 AC rotating machine, 3 position detectionunit, 4 current detection unit, 6 first coordinate conversion unit, 7current control unit, 8 second coordinate conversion unit, 9 voltagecommand generation unit, 10 voltage command output unit, 151 torquedetection unit, 152 current command calculation unit

The invention claimed is:
 1. A control device for an AC rotatingmachine, comprising: a voltage application unit configured to applyvoltages to the AC rotating machine based on voltage command values onstationary coordinates; a current detection unit configured to detectcurrents in a plurality of phases flowing through the AC rotatingmachine; a first coordinate conversion unit configured to set thecurrents detected in the plurality of phases by the current detectionunit as detection currents on the stationary coordinates, and applycoordinate conversion to the detection currents on the stationarycoordinates based on any phase of the AC rotating machine, to therebyoutput detection currents on rotational coordinates; a current controlunit configured to output voltage command values on the rotationalcoordinates based on current command values on the rotationalcoordinates, which specify currents to be supplied to the AC rotatingmachine, and on the detection currents on the rotational coordinates; asecond coordinate conversion unit configured to apply coordinateconversion to the voltage command values on the rotational coordinatesbased on the any phase, to thereby output first voltage command valueson the stationary coordinates; a voltage command generation unitconfigured to set one of the first voltage command values on thestationary coordinates and second voltage command values on thestationary coordinates generated immediately before as target commandvalues, and correct phases of the target command values based on achange rate of the any phase, to thereby generate the second voltagecommand values on the stationary coordinates without using the detectioncurrent; and a voltage command output unit configured to select one ofthe second voltage command values on the stationary coordinatesgenerated by the voltage command generation unit and the first voltagecommand values on the stationary coordinates generated by the secondcoordinate conversion unit, to thereby output the selected one of thesecond voltage command values and the first voltage command values asthe voltage command values on the stationary coordinates.
 2. The controldevice for an AC rotating machine according to claim 1, wherein acalculation cycle of the coordinate conversion to be executed by atleast one of the first coordinate conversion unit or the secondcoordinate conversion unit is longer than an update cycle at which thevoltage command values on the stationary coordinates output by thevoltage command output unit are updated.
 3. The control device for an ACrotating machine according to claim 1, wherein a detection cycle of thedetection of the currents in the plurality of phases by the currentdetection unit is longer than an update cycle at which the voltagecommand values on the stationary coordinates output by the voltagecommand output unit are updated.
 4. The control device for an ACrotating machine according to claim 1, wherein the voltage commandgeneration unit includes: a storage unit configured to store, as thetarget command values, the first voltage command values on thestationary coordinates to be selected by the voltage command output unitas the voltage command values on the stationary coordinates; and avoltage command calculation unit configured to correct the phases of thetarget command values stored in the storage unit based on the changerate, to thereby generate the second voltage command values on thestationary coordinates.
 5. The control device for an AC rotating machineaccording to claim 1, wherein the voltage command generation unitincludes: a storage unit configured to store, as the target commandvalues, the first voltage command values on the stationary coordinatesto be selected by the voltage command output unit as the voltage commandvalues on the stationary coordinates; a plurality of voltage commandcalculation units configured to correct the phases of the target commandvalues stored in the storage unit based on the change rate, to therebygenerate third voltage command values on the stationary coordinates atassumed time points different from one another; and a voltage commandselection unit configured to select one of the third voltage commandvalues on the stationary coordinates generated by the respectiveplurality of voltage command calculation units, to thereby output theselected one of the third voltage command values as the second voltagecommand values on the stationary coordinates.
 6. The control device foran AC rotating machine according to one of claim 1, wherein the voltagecommand generation unit includes: a storage unit configured to store, asthe target command values, the voltage command values on the stationarycoordinates to be output by the voltage command output unit; and avoltage command calculation unit configured to correct the phases of thetarget command values stored in the storage unit based on the changerate, to thereby generate the second voltage command values on thestationary coordinates.
 7. A control device for an electric powersteering, the electric power steering system being configured to use anAC rotating machine as a power source for generating an assist torquefor assisting a steering torque of a vehicle, the control device for theelectric power steering system comprising: the control device for the ACrotating machine of claim 1; a torque detection unit configured todetect the steering torque to output the steering torque as a detectiontorque; and a current command calculation unit configured to generate,based on the detection torque, the current command values on therotational coordinates to be output to the control device for the ACrotating machine.